diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 6326e147a..7dead2ee7 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -58,4 +58,4 @@ jobs:
           distribution: 'zulu'
 
       - name: Android Lint checks
-        run: cd commonmark-android-test && ./gradlew :app:lint
+        run: cd commonmark-android-test && ./gradlew :app:lint && ./gradlew :app:animalsnifferDebug
diff --git a/README.md b/README.md
index 9559a6bcb..8e838e582 100644
--- a/README.md
+++ b/README.md
@@ -26,7 +26,7 @@ extensible library with the following features:
 
 The library is supported on Java 11 and later. It works on Android too,
 but that is on a best-effort basis, please report problems. For Android the
-minimum API level is 19, see the
+minimum API level is 24, see the
 [commonmark-android-test](commonmark-android-test)
 directory.
 
diff --git a/commonmark-android-test/README.md b/commonmark-android-test/README.md
index 0fb792ae3..9b737a98d 100644
--- a/commonmark-android-test/README.md
+++ b/commonmark-android-test/README.md
@@ -6,8 +6,8 @@ Current `minSdk` is 19
 
 Requirements:
 
-* Java 11 or above
-* Android SDK 30
+* Java 17 or above (supported by the Gradle wrapper version)
+* Android SDK Platform 30 and SDK Build Tools 36.0.0
 
 Configuration
 -----
diff --git a/commonmark-android-test/app/build.gradle b/commonmark-android-test/app/build.gradle
index fd8ae34cb..30b7cce8b 100644
--- a/commonmark-android-test/app/build.gradle
+++ b/commonmark-android-test/app/build.gradle
@@ -1,3 +1,8 @@
+// Check Java API usage
+plugins {
+    id 'ru.vyarus.animalsniffer' version '2.0.1'
+}
+
 apply plugin: 'com.android.application'
 
 android {
@@ -6,7 +11,7 @@ android {
 
     defaultConfig {
         applicationId "org.commonmark.android.test"
-        minSdk 19
+        minSdk 24
         targetSdk 30
         versionCode 1
         versionName "1.0"
@@ -49,4 +54,6 @@ android {
 
 dependencies {
     implementation('org.nibor.autolink:autolink:0.11.0')
+
+    signature 'net.sf.androidscents.signature:android-api-level-24:7.0_r2@signature'
 }
diff --git a/commonmark-android-test/build.gradle b/commonmark-android-test/build.gradle
index f359e8154..812dc8e40 100644
--- a/commonmark-android-test/build.gradle
+++ b/commonmark-android-test/build.gradle
@@ -4,7 +4,7 @@ buildscript {
         google()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:7.4.2'
+        classpath 'com.android.tools.build:gradle:9.4.1'
     }
 }
 
diff --git a/commonmark-android-test/gradle/wrapper/gradle-wrapper.jar b/commonmark-android-test/gradle/wrapper/gradle-wrapper.jar
index d64cd4917..9fa7f2882 100644
Binary files a/commonmark-android-test/gradle/wrapper/gradle-wrapper.jar and b/commonmark-android-test/gradle/wrapper/gradle-wrapper.jar differ
diff --git a/commonmark-android-test/gradle/wrapper/gradle-wrapper.properties b/commonmark-android-test/gradle/wrapper/gradle-wrapper.properties
index a80b22ce5..91c4fc64a 100644
--- a/commonmark-android-test/gradle/wrapper/gradle-wrapper.properties
+++ b/commonmark-android-test/gradle/wrapper/gradle-wrapper.properties
@@ -1,7 +1,9 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-8.6-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-9.8.2-bin.zip
 networkTimeout=10000
+retries=0
+retryBackOffMs=500
 validateDistributionUrl=true
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
diff --git a/commonmark-android-test/gradlew b/commonmark-android-test/gradlew
index 1aa94a426..249efbb03 100755
--- a/commonmark-android-test/gradlew
+++ b/commonmark-android-test/gradlew
@@ -1,7 +1,7 @@
 #!/bin/sh
 
 #
-# Copyright © 2015-2021 the original authors.
+# Copyright © 2015 the original authors.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -15,10 +15,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 #
+# SPDX-License-Identifier: Apache-2.0
+#
 
 ##############################################################################
 #
-#   Gradle start up script for POSIX generated by Gradle.
+#   gradlew start up script for POSIX generated by Gradle.
 #
 #   Important for running:
 #
@@ -27,7 +29,7 @@
 #       bash, then to run this script, type that shell name before the whole
 #       command line, like:
 #
-#           ksh Gradle
+#           ksh gradlew
 #
 #       Busybox and similar reduced shells will NOT work, because this script
 #       requires all of these POSIX shell features:
@@ -55,7 +57,7 @@
 #       Darwin, MinGW, and NonStop.
 #
 #   (3) This script is generated from the Groovy template
-#       https://github.com/gradle/gradle/blob/HEAD/subprojects/plugins/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
+#       https://github.com/gradle/gradle/blob/3d91ce3b8caaf77ad09f381f43615b715b53f72c/platforms/jvm/plugins-application/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
 #       within the Gradle project.
 #
 #       You can find Gradle at https://github.com/gradle/gradle/.
@@ -84,7 +86,7 @@ done
 # shellcheck disable=SC2034
 APP_BASE_NAME=${0##*/}
 # Discard cd standard output in case $CDPATH is set (https://github.com/gradle/gradle/issues/25036)
-APP_HOME=$( cd "${APP_HOME:-./}" > /dev/null && pwd -P ) || exit
+APP_HOME=$( cd -P "${APP_HOME:-./}" > /dev/null && printf '%s\n' "$PWD" ) || exit
 
 # Use the maximum available, or set MAX_FD != -1 to use that value.
 MAX_FD=maximum
@@ -112,7 +114,6 @@ case "$( uname )" in                #(
   NONSTOP* )        nonstop=true ;;
 esac
 
-CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
 
 
 # Determine the Java command to use to start the JVM.
@@ -170,7 +171,6 @@ fi
 # For Cygwin or MSYS, switch paths to Windows format before running java
 if "$cygwin" || "$msys" ; then
     APP_HOME=$( cygpath --path --mixed "$APP_HOME" )
-    CLASSPATH=$( cygpath --path --mixed "$CLASSPATH" )
 
     JAVACMD=$( cygpath --unix "$JAVACMD" )
 
@@ -203,15 +203,14 @@ fi
 DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
 
 # Collect all arguments for the java command:
-#   * DEFAULT_JVM_OPTS, JAVA_OPTS, JAVA_OPTS, and optsEnvironmentVar are not allowed to contain shell fragments,
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and optsEnvironmentVar are not allowed to contain shell fragments,
 #     and any embedded shellness will be escaped.
 #   * For example: A user cannot expect ${Hostname} to be expanded, as it is an environment variable and will be
 #     treated as '${Hostname}' itself on the command line.
 
 set -- \
         "-Dorg.gradle.appname=$APP_BASE_NAME" \
-        -classpath "$CLASSPATH" \
-        org.gradle.wrapper.GradleWrapperMain \
+        -jar "$APP_HOME/gradle/wrapper/gradle-wrapper.jar" \
         "$@"
 
 # Stop when "xargs" is not available.
diff --git a/commonmark-android-test/gradlew.bat b/commonmark-android-test/gradlew.bat
index 7101f8e46..03754c4c3 100644
--- a/commonmark-android-test/gradlew.bat
+++ b/commonmark-android-test/gradlew.bat
@@ -13,16 +13,45 @@
 @rem See the License for the specific language governing permissions and
 @rem limitations under the License.
 @rem
+@rem SPDX-License-Identifier: Apache-2.0
+@rem
 
 @if "%DEBUG%"=="" @echo off
 @rem ##########################################################################
 @rem
-@rem  Gradle startup script for Windows
+@rem  gradlew startup script for Windows
 @rem
 @rem ##########################################################################
 
-@rem Set local scope for the variables with windows NT shell
-if "%OS%"=="Windows_NT" setlocal
+@rem Set local scope for the variables, and ensure extensions are enabled
+setlocal EnableExtensions
+
+@rem Catch executions from older scripts and ensure they exit cleanly.
+@rem This can be removed once we can be reasonably confident that few people
+@rem will be migrating directly to this new wrapper.
+goto afterSafetyNet
+::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
+::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
+::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
+::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
+::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
+::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
+::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
+::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
+::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
+::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
+::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
+::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
+::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
+::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
+::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
+::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
+::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
+::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
+::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
+::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
+goto exitWithErrorLevel
+:afterSafetyNet
 
 set DIRNAME=%~dp0
 if "%DIRNAME%"=="" set DIRNAME=.
@@ -43,13 +72,14 @@ set JAVA_EXE=java.exe
 %JAVA_EXE% -version >NUL 2>&1
 if %ERRORLEVEL% equ 0 goto execute
 
-echo. 1>&2
-echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH. 1>&2
-echo. 1>&2
-echo Please set the JAVA_HOME variable in your environment to match the 1>&2
-echo location of your Java installation. 1>&2
+1>&2 echo.
+1>&2 echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+1>&2 echo.
+1>&2 echo Please set the JAVA_HOME variable in your environment to match the
+1>&2 echo location of your Java installation.
 
-goto fail
+"%COMSPEC%" /c exit 1
+goto exitWithErrorLevel
 
 :findJavaFromJavaHome
 set JAVA_HOME=%JAVA_HOME:"=%
@@ -57,36 +87,26 @@ set JAVA_EXE=%JAVA_HOME%/bin/java.exe
 
 if exist "%JAVA_EXE%" goto execute
 
-echo. 1>&2
-echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME% 1>&2
-echo. 1>&2
-echo Please set the JAVA_HOME variable in your environment to match the 1>&2
-echo location of your Java installation. 1>&2
+1>&2 echo.
+1>&2 echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
+1>&2 echo.
+1>&2 echo Please set the JAVA_HOME variable in your environment to match the
+1>&2 echo location of your Java installation.
 
-goto fail
+"%COMSPEC%" /c exit 1
+goto exitWithErrorLevel
 
 :execute
 @rem Setup the command line
 
-set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
-
-
-@rem Execute Gradle
-"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %*
-
-:end
-@rem End local scope for the variables with windows NT shell
-if %ERRORLEVEL% equ 0 goto mainEnd
 
-:fail
-rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
-rem the _cmd.exe /c_ return code!
-set EXIT_CODE=%ERRORLEVEL%
-if %EXIT_CODE% equ 0 set EXIT_CODE=1
-if not ""=="%GRADLE_EXIT_CONSOLE%" exit %EXIT_CODE%
-exit /b %EXIT_CODE%
 
-:mainEnd
-if "%OS%"=="Windows_NT" endlocal
+@rem Execute gradlew
+@rem endlocal doesn't take effect until after the line is parsed and variables are expanded
+@rem which allows us to clear the local environment before executing the java command
+endlocal & "%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -jar "%APP_HOME%\gradle\wrapper\gradle-wrapper.jar" %* & call :exitWithErrorLevel & goto exitWithErrorLevel
 
-:omega
+@rem This label must not be changed. We rely on old scripts being able to jump to this point.
+:exitWithErrorLevel
+@rem Use "%COMSPEC%" /c exit to allow operators to work properly in scripts
+"%COMSPEC%" /c exit %ERRORLEVEL%
diff --git a/commonmark-ext-autolink/src/main/java/org/commonmark/ext/autolink/AutolinkExtension.java b/commonmark-ext-autolink/src/main/java/org/commonmark/ext/autolink/AutolinkExtension.java
index 14222121c..8d24b5769 100644
--- a/commonmark-ext-autolink/src/main/java/org/commonmark/ext/autolink/AutolinkExtension.java
+++ b/commonmark-ext-autolink/src/main/java/org/commonmark/ext/autolink/AutolinkExtension.java
@@ -1,5 +1,6 @@
 package org.commonmark.ext.autolink;
 
+import java.util.Arrays;
 import java.util.EnumSet;
 import java.util.Set;
 import org.commonmark.Extension;
@@ -57,7 +58,12 @@ public Builder linkTypes(AutolinkType... linkTypes) {
                 throw new NullPointerException("linkTypes must not be null");
             }
 
-            return this.linkTypes(Set.of(linkTypes));
+            if (linkTypes.length == 0) {
+                throw new IllegalArgumentException("linkTypes must not be empty");
+            }
+
+            this.linkTypes = EnumSet.copyOf(Arrays.asList(linkTypes));
+            return this;
         }
 
         /**
diff --git a/commonmark-ext-footnotes/src/main/java/org/commonmark/ext/footnotes/FootnotesExtension.java b/commonmark-ext-footnotes/src/main/java/org/commonmark/ext/footnotes/FootnotesExtension.java
index 4517d14d6..f1114249b 100644
--- a/commonmark-ext-footnotes/src/main/java/org/commonmark/ext/footnotes/FootnotesExtension.java
+++ b/commonmark-ext-footnotes/src/main/java/org/commonmark/ext/footnotes/FootnotesExtension.java
@@ -1,5 +1,6 @@
 package org.commonmark.ext.footnotes;
 
+import java.util.Collections;
 import java.util.Set;
 import org.commonmark.Extension;
 import org.commonmark.ext.footnotes.internal.*;
@@ -83,7 +84,7 @@ public NodeRenderer create(MarkdownNodeRendererContext context) {
 
                     @Override
                     public Set<Character> getSpecialCharacters() {
-                        return Set.of();
+                        return Collections.emptySet();
                     }
                 });
     }
diff --git a/commonmark-ext-footnotes/src/main/java/org/commonmark/ext/footnotes/internal/FootnoteBlockParser.java b/commonmark-ext-footnotes/src/main/java/org/commonmark/ext/footnotes/internal/FootnoteBlockParser.java
index db11b906a..2bda7ad0a 100644
--- a/commonmark-ext-footnotes/src/main/java/org/commonmark/ext/footnotes/internal/FootnoteBlockParser.java
+++ b/commonmark-ext-footnotes/src/main/java/org/commonmark/ext/footnotes/internal/FootnoteBlockParser.java
@@ -1,5 +1,6 @@
 package org.commonmark.ext.footnotes.internal;
 
+import java.util.Collections;
 import java.util.List;
 import org.commonmark.ext.footnotes.FootnoteDefinition;
 import org.commonmark.node.Block;
@@ -54,7 +55,7 @@ public BlockContinue tryContinue(ParserState parserState) {
     public List<DefinitionMap<?>> getDefinitions() {
         var map = new DefinitionMap<>(FootnoteDefinition.class);
         map.putIfAbsent(block.getLabel(), block);
-        return List.of(map);
+        return Collections.singletonList(map);
     }
 
     public static class Factory implements BlockParserFactory {
diff --git a/commonmark-ext-footnotes/src/main/java/org/commonmark/ext/footnotes/internal/FootnoteHtmlNodeRenderer.java b/commonmark-ext-footnotes/src/main/java/org/commonmark/ext/footnotes/internal/FootnoteHtmlNodeRenderer.java
index db88a8269..2c2d42513 100644
--- a/commonmark-ext-footnotes/src/main/java/org/commonmark/ext/footnotes/internal/FootnoteHtmlNodeRenderer.java
+++ b/commonmark-ext-footnotes/src/main/java/org/commonmark/ext/footnotes/internal/FootnoteHtmlNodeRenderer.java
@@ -82,7 +82,12 @@ public FootnoteHtmlNodeRenderer(HtmlNodeRendererContext context) {
 
     @Override
     public Set<Class<? extends Node>> getNodeTypes() {
-        return Set.of(FootnoteReference.class, InlineFootnote.class, FootnoteDefinition.class);
+        return Collections.unmodifiableSet(
+                new HashSet<>(
+                        Arrays.asList(
+                                FootnoteReference.class,
+                                InlineFootnote.class,
+                                FootnoteDefinition.class)));
     }
 
     @Override
@@ -203,7 +208,10 @@ private ReferenceInfo registerReference(Node node, String label) {
     }
 
     private void renderReference(Node node, ReferenceInfo referenceInfo) {
-        html.tag("sup", context.extendAttributes(node, "sup", Map.of("class", "footnote-ref")));
+        html.tag(
+                "sup",
+                context.extendAttributes(
+                        node, "sup", Collections.singletonMap("class", "footnote-ref")));
 
         var href = "#" + referenceInfo.definitionId;
         var attrs = new LinkedHashMap<String, String>();
@@ -231,7 +239,7 @@ private void renderDefinition(Node def, ReferencedDefinition referencedDefinitio
                     // Because we're manually rendering the <p> for the last paragraph, do the same
                     // for all other paragraphs for consistency (Paragraph rendering might be
                     // overwritten by a custom renderer).
-                    html.tag("p", context.extendAttributes(node, "p", Map.of()));
+                    html.tag("p", context.extendAttributes(node, "p", Collections.emptyMap()));
                     renderChildren(node);
                     html.tag("/p");
                     html.line();
@@ -241,14 +249,14 @@ private void renderDefinition(Node def, ReferencedDefinition referencedDefinitio
                 node = node.getNext();
             }
 
-            html.tag("p", context.extendAttributes(lastParagraph, "p", Map.of()));
+            html.tag("p", context.extendAttributes(lastParagraph, "p", Collections.emptyMap()));
             renderChildren(lastParagraph);
             html.raw(" ");
             renderBackrefs(def, referencedDefinition);
             html.tag("/p");
             html.line();
         } else if (def instanceof InlineFootnote) {
-            html.tag("p", context.extendAttributes(def, "p", Map.of()));
+            html.tag("p", context.extendAttributes(def, "p", Collections.emptyMap()));
             renderChildren(def);
             html.raw(" ");
             renderBackrefs(def, referencedDefinition);
@@ -283,7 +291,8 @@ private void renderBackrefs(Node def, ReferencedDefinition referencedDefinition)
             if (refNumber > 1) {
                 html.tag(
                         "sup",
-                        context.extendAttributes(def, "sup", Map.of("class", "footnote-ref")));
+                        context.extendAttributes(
+                                def, "sup", Collections.singletonMap("class", "footnote-ref")));
                 html.raw(String.valueOf(refNumber));
                 html.tag("/sup");
             }
diff --git a/commonmark-ext-footnotes/src/main/java/org/commonmark/ext/footnotes/internal/FootnoteMarkdownNodeRenderer.java b/commonmark-ext-footnotes/src/main/java/org/commonmark/ext/footnotes/internal/FootnoteMarkdownNodeRenderer.java
index 0e654cf5e..a812a822d 100644
--- a/commonmark-ext-footnotes/src/main/java/org/commonmark/ext/footnotes/internal/FootnoteMarkdownNodeRenderer.java
+++ b/commonmark-ext-footnotes/src/main/java/org/commonmark/ext/footnotes/internal/FootnoteMarkdownNodeRenderer.java
@@ -1,5 +1,8 @@
 package org.commonmark.ext.footnotes.internal;
 
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashSet;
 import java.util.Set;
 import org.commonmark.ext.footnotes.FootnoteDefinition;
 import org.commonmark.ext.footnotes.FootnoteReference;
@@ -21,7 +24,12 @@ public FootnoteMarkdownNodeRenderer(MarkdownNodeRendererContext context) {
 
     @Override
     public Set<Class<? extends Node>> getNodeTypes() {
-        return Set.of(FootnoteReference.class, InlineFootnote.class, FootnoteDefinition.class);
+        return Collections.unmodifiableSet(
+                new HashSet<>(
+                        Arrays.asList(
+                                FootnoteReference.class,
+                                InlineFootnote.class,
+                                FootnoteDefinition.class)));
     }
 
     @Override
diff --git a/commonmark-ext-gfm-alerts/src/main/java/org/commonmark/ext/gfm/alerts/AlertsExtension.java b/commonmark-ext-gfm-alerts/src/main/java/org/commonmark/ext/gfm/alerts/AlertsExtension.java
index 3035c9952..9c4515855 100644
--- a/commonmark-ext-gfm-alerts/src/main/java/org/commonmark/ext/gfm/alerts/AlertsExtension.java
+++ b/commonmark-ext-gfm-alerts/src/main/java/org/commonmark/ext/gfm/alerts/AlertsExtension.java
@@ -1,5 +1,6 @@
 package org.commonmark.ext.gfm.alerts;
 
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Locale;
@@ -121,7 +122,7 @@ public NodeRenderer create(MarkdownNodeRendererContext context) {
 
                     @Override
                     public Set<Character> getSpecialCharacters() {
-                        return Set.of();
+                        return Collections.emptySet();
                     }
                 });
     }
diff --git a/commonmark-ext-gfm-alerts/src/main/java/org/commonmark/ext/gfm/alerts/internal/AlertBlockParser.java b/commonmark-ext-gfm-alerts/src/main/java/org/commonmark/ext/gfm/alerts/internal/AlertBlockParser.java
index 67acbe475..b5ecd23e2 100644
--- a/commonmark-ext-gfm-alerts/src/main/java/org/commonmark/ext/gfm/alerts/internal/AlertBlockParser.java
+++ b/commonmark-ext-gfm-alerts/src/main/java/org/commonmark/ext/gfm/alerts/internal/AlertBlockParser.java
@@ -1,6 +1,6 @@
 package org.commonmark.ext.gfm.alerts.internal;
 
-import java.util.List;
+import java.util.Collections;
 import java.util.Locale;
 import java.util.Set;
 import java.util.regex.Pattern;
@@ -91,7 +91,7 @@ public void parseInlines(InlineParser inlineParser) {
         // Set source spans on the title node from the source line
         var sourceSpan = titleLine.getSourceSpan();
         if (sourceSpan != null) {
-            titleNode.setSourceSpans(List.of(sourceSpan));
+            titleNode.setSourceSpans(Collections.singletonList(sourceSpan));
         }
 
         // Body blocks were attached as children during block parsing. Prepend the title.
diff --git a/commonmark-ext-gfm-alerts/src/main/java/org/commonmark/ext/gfm/alerts/internal/AlertHtmlNodeRenderer.java b/commonmark-ext-gfm-alerts/src/main/java/org/commonmark/ext/gfm/alerts/internal/AlertHtmlNodeRenderer.java
index 30aea6f04..5f5fe78f8 100644
--- a/commonmark-ext-gfm-alerts/src/main/java/org/commonmark/ext/gfm/alerts/internal/AlertHtmlNodeRenderer.java
+++ b/commonmark-ext-gfm-alerts/src/main/java/org/commonmark/ext/gfm/alerts/internal/AlertHtmlNodeRenderer.java
@@ -1,5 +1,6 @@
 package org.commonmark.ext.gfm.alerts.internal;
 
+import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.Map;
 import org.commonmark.ext.gfm.alerts.Alert;
@@ -40,7 +41,9 @@ protected void renderAlert(Alert alert) {
 
         // Render alert title
         htmlWriter.tag(
-                "p", context.extendAttributes(alert, "p", Map.of("class", "markdown-alert-title")));
+                "p",
+                context.extendAttributes(
+                        alert, "p", Collections.singletonMap("class", "markdown-alert-title")));
         var first = alert.getFirstChild();
         if (first instanceof AlertTitle) {
             renderChildren(first);
diff --git a/commonmark-ext-gfm-alerts/src/main/java/org/commonmark/ext/gfm/alerts/internal/AlertNodeRenderer.java b/commonmark-ext-gfm-alerts/src/main/java/org/commonmark/ext/gfm/alerts/internal/AlertNodeRenderer.java
index ff4bdf6ad..23926bf91 100644
--- a/commonmark-ext-gfm-alerts/src/main/java/org/commonmark/ext/gfm/alerts/internal/AlertNodeRenderer.java
+++ b/commonmark-ext-gfm-alerts/src/main/java/org/commonmark/ext/gfm/alerts/internal/AlertNodeRenderer.java
@@ -1,5 +1,6 @@
 package org.commonmark.ext.gfm.alerts.internal;
 
+import java.util.Collections;
 import java.util.Set;
 import org.commonmark.ext.gfm.alerts.Alert;
 import org.commonmark.ext.gfm.alerts.AlertTitle;
@@ -10,7 +11,7 @@ public abstract class AlertNodeRenderer implements NodeRenderer {
 
     @Override
     public Set<Class<? extends Node>> getNodeTypes() {
-        return Set.of(Alert.class);
+        return Collections.singleton(Alert.class);
     }
 
     @Override
diff --git a/commonmark-ext-gfm-strikethrough/src/main/java/org/commonmark/ext/gfm/strikethrough/StrikethroughExtension.java b/commonmark-ext-gfm-strikethrough/src/main/java/org/commonmark/ext/gfm/strikethrough/StrikethroughExtension.java
index 4b18b7d66..f3b01fee3 100644
--- a/commonmark-ext-gfm-strikethrough/src/main/java/org/commonmark/ext/gfm/strikethrough/StrikethroughExtension.java
+++ b/commonmark-ext-gfm-strikethrough/src/main/java/org/commonmark/ext/gfm/strikethrough/StrikethroughExtension.java
@@ -1,5 +1,6 @@
 package org.commonmark.ext.gfm.strikethrough;
 
+import java.util.Collections;
 import java.util.Set;
 import org.commonmark.Extension;
 import org.commonmark.ext.gfm.strikethrough.internal.StrikethroughDelimiterProcessor;
@@ -96,7 +97,7 @@ public NodeRenderer create(MarkdownNodeRendererContext context) {
 
                     @Override
                     public Set<Character> getSpecialCharacters() {
-                        return Set.of('~');
+                        return Collections.singleton('~');
                     }
                 });
     }
diff --git a/commonmark-ext-gfm-strikethrough/src/main/java/org/commonmark/ext/gfm/strikethrough/internal/StrikethroughHtmlNodeRenderer.java b/commonmark-ext-gfm-strikethrough/src/main/java/org/commonmark/ext/gfm/strikethrough/internal/StrikethroughHtmlNodeRenderer.java
index e5ee31f4e..033258d7c 100644
--- a/commonmark-ext-gfm-strikethrough/src/main/java/org/commonmark/ext/gfm/strikethrough/internal/StrikethroughHtmlNodeRenderer.java
+++ b/commonmark-ext-gfm-strikethrough/src/main/java/org/commonmark/ext/gfm/strikethrough/internal/StrikethroughHtmlNodeRenderer.java
@@ -1,5 +1,6 @@
 package org.commonmark.ext.gfm.strikethrough.internal;
 
+import java.util.Collections;
 import java.util.Map;
 import org.commonmark.node.Node;
 import org.commonmark.renderer.html.HtmlNodeRendererContext;
@@ -17,7 +18,8 @@ public StrikethroughHtmlNodeRenderer(HtmlNodeRendererContext context) {
 
     @Override
     public void render(Node node) {
-        Map<String, String> attributes = context.extendAttributes(node, "del", Map.of());
+        Map<String, String> attributes =
+                context.extendAttributes(node, "del", Collections.emptyMap());
         html.tag("del", attributes);
         renderChildren(node);
         html.tag("/del");
diff --git a/commonmark-ext-gfm-strikethrough/src/main/java/org/commonmark/ext/gfm/strikethrough/internal/StrikethroughNodeRenderer.java b/commonmark-ext-gfm-strikethrough/src/main/java/org/commonmark/ext/gfm/strikethrough/internal/StrikethroughNodeRenderer.java
index 56d94d300..1c4254671 100644
--- a/commonmark-ext-gfm-strikethrough/src/main/java/org/commonmark/ext/gfm/strikethrough/internal/StrikethroughNodeRenderer.java
+++ b/commonmark-ext-gfm-strikethrough/src/main/java/org/commonmark/ext/gfm/strikethrough/internal/StrikethroughNodeRenderer.java
@@ -1,5 +1,6 @@
 package org.commonmark.ext.gfm.strikethrough.internal;
 
+import java.util.Collections;
 import java.util.Set;
 import org.commonmark.ext.gfm.strikethrough.Strikethrough;
 import org.commonmark.node.Node;
@@ -9,6 +10,6 @@ abstract class StrikethroughNodeRenderer implements NodeRenderer {
 
     @Override
     public Set<Class<? extends Node>> getNodeTypes() {
-        return Set.of(Strikethrough.class);
+        return Collections.singleton(Strikethrough.class);
     }
 }
diff --git a/commonmark-ext-gfm-tables/src/main/java/org/commonmark/ext/gfm/tables/TablesExtension.java b/commonmark-ext-gfm-tables/src/main/java/org/commonmark/ext/gfm/tables/TablesExtension.java
index 0db0ea513..4646c18dd 100644
--- a/commonmark-ext-gfm-tables/src/main/java/org/commonmark/ext/gfm/tables/TablesExtension.java
+++ b/commonmark-ext-gfm-tables/src/main/java/org/commonmark/ext/gfm/tables/TablesExtension.java
@@ -1,5 +1,6 @@
 package org.commonmark.ext.gfm.tables;
 
+import java.util.Collections;
 import java.util.Set;
 import org.commonmark.Extension;
 import org.commonmark.ext.gfm.tables.internal.TableBlockParser;
@@ -78,7 +79,7 @@ public NodeRenderer create(MarkdownNodeRendererContext context) {
 
                     @Override
                     public Set<Character> getSpecialCharacters() {
-                        return Set.of('|');
+                        return Collections.singleton('|');
                     }
                 });
     }
diff --git a/commonmark-ext-gfm-tables/src/main/java/org/commonmark/ext/gfm/tables/internal/TableHtmlNodeRenderer.java b/commonmark-ext-gfm-tables/src/main/java/org/commonmark/ext/gfm/tables/internal/TableHtmlNodeRenderer.java
index 81e584c9d..d0039d41d 100644
--- a/commonmark-ext-gfm-tables/src/main/java/org/commonmark/ext/gfm/tables/internal/TableHtmlNodeRenderer.java
+++ b/commonmark-ext-gfm-tables/src/main/java/org/commonmark/ext/gfm/tables/internal/TableHtmlNodeRenderer.java
@@ -1,5 +1,6 @@
 package org.commonmark.ext.gfm.tables.internal;
 
+import java.util.Collections;
 import java.util.Map;
 import org.commonmark.ext.gfm.tables.*;
 import org.commonmark.node.Node;
@@ -63,15 +64,17 @@ protected void renderCell(TableCell tableCell) {
     }
 
     private Map<String, String> getAttributes(Node node, String tagName) {
-        return context.extendAttributes(node, tagName, Map.of());
+        return context.extendAttributes(node, tagName, Collections.emptyMap());
     }
 
     private Map<String, String> getCellAttributes(TableCell tableCell, String tagName) {
         if (tableCell.getAlignment() != null) {
             return context.extendAttributes(
-                    tableCell, tagName, Map.of("align", getAlignValue(tableCell.getAlignment())));
+                    tableCell,
+                    tagName,
+                    Collections.singletonMap("align", getAlignValue(tableCell.getAlignment())));
         } else {
-            return context.extendAttributes(tableCell, tagName, Map.of());
+            return context.extendAttributes(tableCell, tagName, Collections.emptyMap());
         }
     }
 
diff --git a/commonmark-ext-gfm-tables/src/main/java/org/commonmark/ext/gfm/tables/internal/TableNodeRenderer.java b/commonmark-ext-gfm-tables/src/main/java/org/commonmark/ext/gfm/tables/internal/TableNodeRenderer.java
index 4e3a00815..3cfe17441 100644
--- a/commonmark-ext-gfm-tables/src/main/java/org/commonmark/ext/gfm/tables/internal/TableNodeRenderer.java
+++ b/commonmark-ext-gfm-tables/src/main/java/org/commonmark/ext/gfm/tables/internal/TableNodeRenderer.java
@@ -1,5 +1,8 @@
 package org.commonmark.ext.gfm.tables.internal;
 
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashSet;
 import java.util.Set;
 import org.commonmark.ext.gfm.tables.*;
 import org.commonmark.node.Node;
@@ -9,12 +12,14 @@ abstract class TableNodeRenderer implements NodeRenderer {
 
     @Override
     public Set<Class<? extends Node>> getNodeTypes() {
-        return Set.of(
-                TableBlock.class,
-                TableHead.class,
-                TableBody.class,
-                TableRow.class,
-                TableCell.class);
+        return Collections.unmodifiableSet(
+                new HashSet<>(
+                        Arrays.asList(
+                                TableBlock.class,
+                                TableHead.class,
+                                TableBody.class,
+                                TableRow.class,
+                                TableCell.class)));
     }
 
     @Override
diff --git a/commonmark-ext-image-attributes/src/main/java/org/commonmark/ext/image/attributes/internal/ImageAttributesDelimiterProcessor.java b/commonmark-ext-image-attributes/src/main/java/org/commonmark/ext/image/attributes/internal/ImageAttributesDelimiterProcessor.java
index 53ba882c9..e7a3062e4 100644
--- a/commonmark-ext-image-attributes/src/main/java/org/commonmark/ext/image/attributes/internal/ImageAttributesDelimiterProcessor.java
+++ b/commonmark-ext-image-attributes/src/main/java/org/commonmark/ext/image/attributes/internal/ImageAttributesDelimiterProcessor.java
@@ -12,7 +12,8 @@
 public class ImageAttributesDelimiterProcessor implements DelimiterProcessor {
 
     // Only allow a defined set of attributes to be used.
-    private static final Set<String> SUPPORTED_ATTRIBUTES = Set.of("width", "height");
+    private static final Set<String> SUPPORTED_ATTRIBUTES =
+            Collections.unmodifiableSet(new HashSet<>(Arrays.asList("width", "height")));
 
     @Override
     public char getOpeningCharacter() {
diff --git a/commonmark-ext-ins/src/main/java/org/commonmark/ext/ins/InsExtension.java b/commonmark-ext-ins/src/main/java/org/commonmark/ext/ins/InsExtension.java
index a39b77af8..b180e5db5 100644
--- a/commonmark-ext-ins/src/main/java/org/commonmark/ext/ins/InsExtension.java
+++ b/commonmark-ext-ins/src/main/java/org/commonmark/ext/ins/InsExtension.java
@@ -1,5 +1,6 @@
 package org.commonmark.ext.ins;
 
+import java.util.Collections;
 import java.util.Set;
 import org.commonmark.Extension;
 import org.commonmark.ext.ins.internal.InsDelimiterProcessor;
@@ -64,7 +65,7 @@ public Set<Character> getSpecialCharacters() {
                         // We technically don't need to escape single occurrences of +, but that's
                         // all the extension API
                         // exposes currently.
-                        return Set.of('+');
+                        return Collections.singleton('+');
                     }
                 });
     }
diff --git a/commonmark-ext-ins/src/main/java/org/commonmark/ext/ins/internal/InsHtmlNodeRenderer.java b/commonmark-ext-ins/src/main/java/org/commonmark/ext/ins/internal/InsHtmlNodeRenderer.java
index d4defcbdc..c4e55dd9f 100644
--- a/commonmark-ext-ins/src/main/java/org/commonmark/ext/ins/internal/InsHtmlNodeRenderer.java
+++ b/commonmark-ext-ins/src/main/java/org/commonmark/ext/ins/internal/InsHtmlNodeRenderer.java
@@ -1,5 +1,6 @@
 package org.commonmark.ext.ins.internal;
 
+import java.util.Collections;
 import java.util.Map;
 import org.commonmark.node.Node;
 import org.commonmark.renderer.html.HtmlNodeRendererContext;
@@ -17,7 +18,8 @@ public InsHtmlNodeRenderer(HtmlNodeRendererContext context) {
 
     @Override
     public void render(Node node) {
-        Map<String, String> attributes = context.extendAttributes(node, "ins", Map.of());
+        Map<String, String> attributes =
+                context.extendAttributes(node, "ins", Collections.emptyMap());
         html.tag("ins", attributes);
         renderChildren(node);
         html.tag("/ins");
diff --git a/commonmark-ext-ins/src/main/java/org/commonmark/ext/ins/internal/InsNodeRenderer.java b/commonmark-ext-ins/src/main/java/org/commonmark/ext/ins/internal/InsNodeRenderer.java
index 4e8e0283e..a31102f91 100644
--- a/commonmark-ext-ins/src/main/java/org/commonmark/ext/ins/internal/InsNodeRenderer.java
+++ b/commonmark-ext-ins/src/main/java/org/commonmark/ext/ins/internal/InsNodeRenderer.java
@@ -1,5 +1,6 @@
 package org.commonmark.ext.ins.internal;
 
+import java.util.Collections;
 import java.util.Set;
 import org.commonmark.ext.ins.Ins;
 import org.commonmark.node.Node;
@@ -9,6 +10,6 @@ abstract class InsNodeRenderer implements NodeRenderer {
 
     @Override
     public Set<Class<? extends Node>> getNodeTypes() {
-        return Set.of(Ins.class);
+        return Collections.singleton(Ins.class);
     }
 }
diff --git a/commonmark-ext-task-list-items/src/main/java/org/commonmark/ext/task/list/items/TaskListItemsExtension.java b/commonmark-ext-task-list-items/src/main/java/org/commonmark/ext/task/list/items/TaskListItemsExtension.java
index abddc519a..efbee4f15 100644
--- a/commonmark-ext-task-list-items/src/main/java/org/commonmark/ext/task/list/items/TaskListItemsExtension.java
+++ b/commonmark-ext-task-list-items/src/main/java/org/commonmark/ext/task/list/items/TaskListItemsExtension.java
@@ -1,5 +1,6 @@
 package org.commonmark.ext.task.list.items;
 
+import java.util.Collections;
 import java.util.Set;
 import org.commonmark.Extension;
 import org.commonmark.ext.task.list.items.internal.TaskListItemHtmlNodeRenderer;
@@ -53,7 +54,7 @@ public NodeRenderer create(MarkdownNodeRendererContext context) {
 
                     @Override
                     public Set<Character> getSpecialCharacters() {
-                        return Set.of();
+                        return Collections.emptySet();
                     }
                 });
     }
diff --git a/commonmark-ext-task-list-items/src/main/java/org/commonmark/ext/task/list/items/internal/TaskListItemNodeRenderer.java b/commonmark-ext-task-list-items/src/main/java/org/commonmark/ext/task/list/items/internal/TaskListItemNodeRenderer.java
index 24efd4e7d..087ab9d27 100644
--- a/commonmark-ext-task-list-items/src/main/java/org/commonmark/ext/task/list/items/internal/TaskListItemNodeRenderer.java
+++ b/commonmark-ext-task-list-items/src/main/java/org/commonmark/ext/task/list/items/internal/TaskListItemNodeRenderer.java
@@ -1,5 +1,6 @@
 package org.commonmark.ext.task.list.items.internal;
 
+import java.util.Collections;
 import java.util.Set;
 import org.commonmark.ext.task.list.items.TaskListItemMarker;
 import org.commonmark.node.Node;
@@ -8,6 +9,6 @@
 public abstract class TaskListItemNodeRenderer implements NodeRenderer {
     @Override
     public Set<Class<? extends Node>> getNodeTypes() {
-        return Set.of(TaskListItemMarker.class);
+        return Collections.singleton(TaskListItemMarker.class);
     }
 }
diff --git a/commonmark-ext-yaml-front-matter/src/main/java/org/commonmark/ext/front/matter/YamlFrontMatterExtension.java b/commonmark-ext-yaml-front-matter/src/main/java/org/commonmark/ext/front/matter/YamlFrontMatterExtension.java
index 0617c8270..55234819d 100644
--- a/commonmark-ext-yaml-front-matter/src/main/java/org/commonmark/ext/front/matter/YamlFrontMatterExtension.java
+++ b/commonmark-ext-yaml-front-matter/src/main/java/org/commonmark/ext/front/matter/YamlFrontMatterExtension.java
@@ -1,5 +1,6 @@
 package org.commonmark.ext.front.matter;
 
+import java.util.Collections;
 import java.util.Objects;
 import java.util.Set;
 import org.commonmark.Extension;
@@ -69,7 +70,7 @@ public NodeRenderer create(MarkdownNodeRendererContext context) {
 
                     @Override
                     public Set<Character> getSpecialCharacters() {
-                        return Set.of();
+                        return Collections.emptySet();
                     }
                 });
     }
diff --git a/commonmark-ext-yaml-front-matter/src/main/java/org/commonmark/ext/front/matter/internal/YamlFrontMatterNodeRenderer.java b/commonmark-ext-yaml-front-matter/src/main/java/org/commonmark/ext/front/matter/internal/YamlFrontMatterNodeRenderer.java
index 607b621ec..53486d0c3 100644
--- a/commonmark-ext-yaml-front-matter/src/main/java/org/commonmark/ext/front/matter/internal/YamlFrontMatterNodeRenderer.java
+++ b/commonmark-ext-yaml-front-matter/src/main/java/org/commonmark/ext/front/matter/internal/YamlFrontMatterNodeRenderer.java
@@ -1,5 +1,6 @@
 package org.commonmark.ext.front.matter.internal;
 
+import java.util.Collections;
 import java.util.Set;
 import org.commonmark.ext.front.matter.YamlFrontMatterBlock;
 import org.commonmark.node.Node;
@@ -8,6 +9,6 @@
 abstract class YamlFrontMatterNodeRenderer implements NodeRenderer {
     @Override
     public Set<Class<? extends Node>> getNodeTypes() {
-        return Set.of(YamlFrontMatterBlock.class);
+        return Collections.singleton(YamlFrontMatterBlock.class);
     }
 }
diff --git a/commonmark/src/main/java/org/commonmark/internal/DocumentParser.java b/commonmark/src/main/java/org/commonmark/internal/DocumentParser.java
index 62b392b88..3724a8cf6 100644
--- a/commonmark/src/main/java/org/commonmark/internal/DocumentParser.java
+++ b/commonmark/src/main/java/org/commonmark/internal/DocumentParser.java
@@ -20,7 +20,7 @@ public class DocumentParser implements ParserState {
 
     private static final Set<Class<? extends Block>> CORE_FACTORY_TYPES =
             new LinkedHashSet<>(
-                    List.of(
+                    Arrays.asList(
                             BlockQuote.class,
                             Heading.class,
                             FencedCodeBlock.class,
diff --git a/commonmark/src/main/java/org/commonmark/internal/InlineParserImpl.java b/commonmark/src/main/java/org/commonmark/internal/InlineParserImpl.java
index e11e493f3..ffa2b51b4 100644
--- a/commonmark/src/main/java/org/commonmark/internal/InlineParserImpl.java
+++ b/commonmark/src/main/java/org/commonmark/internal/InlineParserImpl.java
@@ -90,7 +90,11 @@ private static Map<Character, DelimiterProcessor> calculateDelimiterProcessors(
             List<DelimiterProcessor> delimiterProcessors) {
         var map = new HashMap<Character, DelimiterProcessor>();
         addDelimiterProcessors(
-                List.of(new AsteriskDelimiterProcessor(), new UnderscoreDelimiterProcessor()), map);
+                Collections.unmodifiableList(
+                        Arrays.asList(
+                                new AsteriskDelimiterProcessor(),
+                                new UnderscoreDelimiterProcessor())),
+                map);
         addDelimiterProcessors(delimiterProcessors, map);
         return map;
     }
@@ -223,11 +227,11 @@ private List<? extends Node> parseInline() {
 
         switch (c) {
             case '[':
-                return List.of(parseOpenBracket());
+                return Collections.singletonList(parseOpenBracket());
             case ']':
-                return List.of(parseCloseBracket());
+                return Collections.singletonList(parseCloseBracket());
             case '\n':
-                return List.of(parseLineBreak());
+                return Collections.singletonList(parseLineBreak());
             case Scanner.END:
                 return null;
         }
@@ -244,7 +248,7 @@ private List<? extends Node> parseInline() {
 
         // No inline parser, delimiter or other special handling.
         if (!specialCharacters.get(c)) {
-            return List.of(parseText());
+            return Collections.singletonList(parseText());
         }
 
         List<InlineContentParser> inlineParsers = this.inlineParsers.get(c);
@@ -260,7 +264,7 @@ private List<? extends Node> parseInline() {
                         node.setSourceSpans(
                                 scanner.getSource(position, scanner.position()).getSourceSpans());
                     }
-                    return List.of(node);
+                    return Collections.singletonList(node);
                 } else {
                     // Reset position
                     scanner.setPosition(position);
@@ -277,7 +281,7 @@ private List<? extends Node> parseInline() {
         }
 
         // If we get here, even for a special/delimiter character, we will just treat it as text.
-        return List.of(parseText());
+        return Collections.singletonList(parseText());
     }
 
     /** Attempt to parse delimiters like emphasis, strong emphasis or custom delimiters. */
@@ -334,7 +338,7 @@ private List<? extends Node> parseLinkMarker() {
                             contentPosition,
                             lastBracket,
                             lastDelimiter));
-            return List.of(bangNode, bracketNode);
+            return Collections.unmodifiableList(Arrays.asList(bangNode, bracketNode));
         } else {
             return null;
         }
diff --git a/commonmark/src/main/java/org/commonmark/internal/ParagraphParser.java b/commonmark/src/main/java/org/commonmark/internal/ParagraphParser.java
index 47f69b34a..9a1e5ec1a 100644
--- a/commonmark/src/main/java/org/commonmark/internal/ParagraphParser.java
+++ b/commonmark/src/main/java/org/commonmark/internal/ParagraphParser.java
@@ -1,5 +1,6 @@
 package org.commonmark.internal;
 
+import java.util.Collections;
 import java.util.List;
 import org.commonmark.node.*;
 import org.commonmark.parser.InlineParser;
@@ -52,7 +53,7 @@ public List<DefinitionMap<?>> getDefinitions() {
         for (var def : linkReferenceDefinitionParser.getDefinitions()) {
             map.putIfAbsent(def.getLabel(), def);
         }
-        return List.of(map);
+        return Collections.singletonList(map);
     }
 
     @Override
diff --git a/commonmark/src/main/java/org/commonmark/internal/inline/AutolinkInlineParser.java b/commonmark/src/main/java/org/commonmark/internal/inline/AutolinkInlineParser.java
index f84a62210..1bd631469 100644
--- a/commonmark/src/main/java/org/commonmark/internal/inline/AutolinkInlineParser.java
+++ b/commonmark/src/main/java/org/commonmark/internal/inline/AutolinkInlineParser.java
@@ -1,5 +1,6 @@
 package org.commonmark.internal.inline;
 
+import java.util.Collections;
 import java.util.Set;
 import java.util.regex.Pattern;
 import org.commonmark.node.Link;
@@ -56,7 +57,7 @@ public ParsedInline tryParse(InlineParserState inlineParserState) {
     public static class Factory implements InlineContentParserFactory {
         @Override
         public Set<Character> getTriggerCharacters() {
-            return Set.of('<');
+            return Collections.singleton('<');
         }
 
         @Override
diff --git a/commonmark/src/main/java/org/commonmark/internal/inline/BackslashInlineParser.java b/commonmark/src/main/java/org/commonmark/internal/inline/BackslashInlineParser.java
index c4e8f3aff..c639606a0 100644
--- a/commonmark/src/main/java/org/commonmark/internal/inline/BackslashInlineParser.java
+++ b/commonmark/src/main/java/org/commonmark/internal/inline/BackslashInlineParser.java
@@ -1,5 +1,6 @@
 package org.commonmark.internal.inline;
 
+import java.util.Collections;
 import java.util.Set;
 import java.util.regex.Pattern;
 import org.commonmark.internal.util.Escaping;
@@ -37,7 +38,7 @@ public ParsedInline tryParse(InlineParserState inlineParserState) {
     public static class Factory implements InlineContentParserFactory {
         @Override
         public Set<Character> getTriggerCharacters() {
-            return Set.of('\\');
+            return Collections.singleton('\\');
         }
 
         @Override
diff --git a/commonmark/src/main/java/org/commonmark/internal/inline/BackticksInlineParser.java b/commonmark/src/main/java/org/commonmark/internal/inline/BackticksInlineParser.java
index 73e5398bf..89b862571 100644
--- a/commonmark/src/main/java/org/commonmark/internal/inline/BackticksInlineParser.java
+++ b/commonmark/src/main/java/org/commonmark/internal/inline/BackticksInlineParser.java
@@ -1,5 +1,6 @@
 package org.commonmark.internal.inline;
 
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.Set;
@@ -77,7 +78,7 @@ public ParsedInline tryParse(InlineParserState inlineParserState) {
     public static class Factory implements InlineContentParserFactory {
         @Override
         public Set<Character> getTriggerCharacters() {
-            return Set.of('`');
+            return Collections.singleton('`');
         }
 
         @Override
diff --git a/commonmark/src/main/java/org/commonmark/internal/inline/EntityInlineParser.java b/commonmark/src/main/java/org/commonmark/internal/inline/EntityInlineParser.java
index e3ed0c08b..a639fc832 100644
--- a/commonmark/src/main/java/org/commonmark/internal/inline/EntityInlineParser.java
+++ b/commonmark/src/main/java/org/commonmark/internal/inline/EntityInlineParser.java
@@ -1,5 +1,6 @@
 package org.commonmark.internal.inline;
 
+import java.util.Collections;
 import java.util.Set;
 import org.commonmark.internal.util.Html5Entities;
 import org.commonmark.node.Text;
@@ -58,7 +59,7 @@ public static class Factory implements InlineContentParserFactory {
 
         @Override
         public Set<Character> getTriggerCharacters() {
-            return Set.of('&');
+            return Collections.singleton('&');
         }
 
         @Override
diff --git a/commonmark/src/main/java/org/commonmark/internal/inline/HtmlInlineParser.java b/commonmark/src/main/java/org/commonmark/internal/inline/HtmlInlineParser.java
index a34346da0..babcb90fb 100644
--- a/commonmark/src/main/java/org/commonmark/internal/inline/HtmlInlineParser.java
+++ b/commonmark/src/main/java/org/commonmark/internal/inline/HtmlInlineParser.java
@@ -1,5 +1,6 @@
 package org.commonmark.internal.inline;
 
+import java.util.Collections;
 import java.util.Set;
 import org.commonmark.node.HtmlInline;
 import org.commonmark.parser.beta.*;
@@ -260,7 +261,7 @@ public static class Factory implements InlineContentParserFactory {
 
         @Override
         public Set<Character> getTriggerCharacters() {
-            return Set.of('<');
+            return Collections.singleton('<');
         }
 
         @Override
diff --git a/commonmark/src/main/java/org/commonmark/node/Node.java b/commonmark/src/main/java/org/commonmark/node/Node.java
index adc64838c..06804bc3e 100644
--- a/commonmark/src/main/java/org/commonmark/node/Node.java
+++ b/commonmark/src/main/java/org/commonmark/node/Node.java
@@ -120,7 +120,9 @@ public void insertBefore(Node sibling) {
      * @since 0.16.0
      */
     public List<SourceSpan> getSourceSpans() {
-        return sourceSpans != null ? Collections.unmodifiableList(sourceSpans) : List.of();
+        return sourceSpans != null
+                ? Collections.unmodifiableList(sourceSpans)
+                : Collections.emptyList();
     }
 
     /**
diff --git a/commonmark/src/main/java/org/commonmark/node/SourceSpans.java b/commonmark/src/main/java/org/commonmark/node/SourceSpans.java
index 945f1c19a..a13053606 100644
--- a/commonmark/src/main/java/org/commonmark/node/SourceSpans.java
+++ b/commonmark/src/main/java/org/commonmark/node/SourceSpans.java
@@ -1,6 +1,7 @@
 package org.commonmark.node;
 
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 
 /**
@@ -17,7 +18,7 @@ public static SourceSpans empty() {
     }
 
     public List<SourceSpan> getSourceSpans() {
-        return sourceSpans != null ? sourceSpans : List.of();
+        return sourceSpans != null ? sourceSpans : Collections.emptyList();
     }
 
     public void addAllFrom(Iterable<? extends Node> nodes) {
diff --git a/commonmark/src/main/java/org/commonmark/parser/block/AbstractBlockParser.java b/commonmark/src/main/java/org/commonmark/parser/block/AbstractBlockParser.java
index 69610a664..9e6861dee 100644
--- a/commonmark/src/main/java/org/commonmark/parser/block/AbstractBlockParser.java
+++ b/commonmark/src/main/java/org/commonmark/parser/block/AbstractBlockParser.java
@@ -1,5 +1,6 @@
 package org.commonmark.parser.block;
 
+import java.util.Collections;
 import java.util.List;
 import org.commonmark.node.Block;
 import org.commonmark.node.DefinitionMap;
@@ -34,7 +35,7 @@ public void addSourceSpan(SourceSpan sourceSpan) {
 
     @Override
     public List<DefinitionMap<?>> getDefinitions() {
-        return List.of();
+        return Collections.emptyList();
     }
 
     @Override
diff --git a/commonmark/src/main/java/org/commonmark/renderer/html/CoreHtmlNodeRenderer.java b/commonmark/src/main/java/org/commonmark/renderer/html/CoreHtmlNodeRenderer.java
index d5e0d8afc..418bf606d 100644
--- a/commonmark/src/main/java/org/commonmark/renderer/html/CoreHtmlNodeRenderer.java
+++ b/commonmark/src/main/java/org/commonmark/renderer/html/CoreHtmlNodeRenderer.java
@@ -1,5 +1,8 @@
 package org.commonmark.renderer.html;
 
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashSet;
 import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.Set;
@@ -21,27 +24,29 @@ public CoreHtmlNodeRenderer(HtmlNodeRendererContext context) {
 
     @Override
     public Set<Class<? extends Node>> getNodeTypes() {
-        return Set.of(
-                Document.class,
-                Heading.class,
-                Paragraph.class,
-                BlockQuote.class,
-                BulletList.class,
-                FencedCodeBlock.class,
-                HtmlBlock.class,
-                ThematicBreak.class,
-                IndentedCodeBlock.class,
-                Link.class,
-                ListItem.class,
-                OrderedList.class,
-                Image.class,
-                Emphasis.class,
-                StrongEmphasis.class,
-                Text.class,
-                Code.class,
-                HtmlInline.class,
-                SoftLineBreak.class,
-                HardLineBreak.class);
+        return Collections.unmodifiableSet(
+                new HashSet<>(
+                        Arrays.asList(
+                                Document.class,
+                                Heading.class,
+                                Paragraph.class,
+                                BlockQuote.class,
+                                BulletList.class,
+                                FencedCodeBlock.class,
+                                HtmlBlock.class,
+                                ThematicBreak.class,
+                                IndentedCodeBlock.class,
+                                Link.class,
+                                ListItem.class,
+                                OrderedList.class,
+                                Image.class,
+                                Emphasis.class,
+                                StrongEmphasis.class,
+                                Text.class,
+                                Code.class,
+                                HtmlInline.class,
+                                SoftLineBreak.class,
+                                HardLineBreak.class)));
     }
 
     @Override
@@ -140,7 +145,7 @@ public void visit(ThematicBreak thematicBreak) {
 
     @Override
     public void visit(IndentedCodeBlock indentedCodeBlock) {
-        renderCodeBlock(indentedCodeBlock.getLiteral(), indentedCodeBlock, Map.of());
+        renderCodeBlock(indentedCodeBlock.getLiteral(), indentedCodeBlock, Collections.emptyMap());
     }
 
     @Override
@@ -294,7 +299,7 @@ private boolean isInTightList(Paragraph paragraph) {
     }
 
     private Map<String, String> getAttrs(Node node, String tagName) {
-        return getAttrs(node, tagName, Map.of());
+        return getAttrs(node, tagName, Collections.emptyMap());
     }
 
     private Map<String, String> getAttrs(
diff --git a/commonmark/src/main/java/org/commonmark/renderer/html/DefaultUrlSanitizer.java b/commonmark/src/main/java/org/commonmark/renderer/html/DefaultUrlSanitizer.java
index bdf59e809..a0a439b63 100644
--- a/commonmark/src/main/java/org/commonmark/renderer/html/DefaultUrlSanitizer.java
+++ b/commonmark/src/main/java/org/commonmark/renderer/html/DefaultUrlSanitizer.java
@@ -11,7 +11,7 @@ public class DefaultUrlSanitizer implements UrlSanitizer {
     private Set<String> protocols;
 
     public DefaultUrlSanitizer() {
-        this(List.of("http", "https", "mailto", "data"));
+        this(Collections.unmodifiableList(Arrays.asList("http", "https", "mailto", "data")));
     }
 
     public DefaultUrlSanitizer(Collection<String> protocols) {
diff --git a/commonmark/src/main/java/org/commonmark/renderer/html/HtmlWriter.java b/commonmark/src/main/java/org/commonmark/renderer/html/HtmlWriter.java
index ebe638dc3..0b3255c9c 100644
--- a/commonmark/src/main/java/org/commonmark/renderer/html/HtmlWriter.java
+++ b/commonmark/src/main/java/org/commonmark/renderer/html/HtmlWriter.java
@@ -1,13 +1,14 @@
 package org.commonmark.renderer.html;
 
 import java.io.IOException;
+import java.util.Collections;
 import java.util.Map;
 import java.util.Objects;
 import org.commonmark.internal.util.Escaping;
 
 public class HtmlWriter {
 
-    private static final Map<String, String> NO_ATTRIBUTES = Map.of();
+    private static final Map<String, String> NO_ATTRIBUTES = Collections.emptyMap();
 
     private final Appendable buffer;
     private char lastChar = 0;
diff --git a/commonmark/src/main/java/org/commonmark/renderer/markdown/CoreMarkdownNodeRenderer.java b/commonmark/src/main/java/org/commonmark/renderer/markdown/CoreMarkdownNodeRenderer.java
index d4025128b..1c6ee2572 100644
--- a/commonmark/src/main/java/org/commonmark/renderer/markdown/CoreMarkdownNodeRenderer.java
+++ b/commonmark/src/main/java/org/commonmark/renderer/markdown/CoreMarkdownNodeRenderer.java
@@ -1,5 +1,8 @@
 package org.commonmark.renderer.markdown;
 
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 import java.util.regex.Matcher;
@@ -54,27 +57,29 @@ public CoreMarkdownNodeRenderer(MarkdownNodeRendererContext context) {
 
     @Override
     public Set<Class<? extends Node>> getNodeTypes() {
-        return Set.of(
-                BlockQuote.class,
-                BulletList.class,
-                Code.class,
-                Document.class,
-                Emphasis.class,
-                FencedCodeBlock.class,
-                HardLineBreak.class,
-                Heading.class,
-                HtmlBlock.class,
-                HtmlInline.class,
-                Image.class,
-                IndentedCodeBlock.class,
-                Link.class,
-                ListItem.class,
-                OrderedList.class,
-                Paragraph.class,
-                SoftLineBreak.class,
-                StrongEmphasis.class,
-                Text.class,
-                ThematicBreak.class);
+        return Collections.unmodifiableSet(
+                new HashSet<>(
+                        Arrays.asList(
+                                BlockQuote.class,
+                                BulletList.class,
+                                Code.class,
+                                Document.class,
+                                Emphasis.class,
+                                FencedCodeBlock.class,
+                                HardLineBreak.class,
+                                Heading.class,
+                                HtmlBlock.class,
+                                HtmlInline.class,
+                                Image.class,
+                                IndentedCodeBlock.class,
+                                Link.class,
+                                ListItem.class,
+                                OrderedList.class,
+                                Paragraph.class,
+                                SoftLineBreak.class,
+                                StrongEmphasis.class,
+                                Text.class,
+                                ThematicBreak.class)));
     }
 
     @Override
@@ -505,9 +510,9 @@ private static List<String> getLines(String literal) {
         if (parts[parts.length - 1].isEmpty()) {
             // But we don't want the last empty string, as "\n" is used as a line terminator (not a
             // separator), so return without the last element.
-            return List.of(parts).subList(0, parts.length - 1);
+            return Collections.unmodifiableList(Arrays.asList(parts)).subList(0, parts.length - 1);
         } else {
-            return List.of(parts);
+            return Collections.unmodifiableList(Arrays.asList(parts));
         }
     }
 
diff --git a/commonmark/src/main/java/org/commonmark/renderer/markdown/MarkdownRenderer.java b/commonmark/src/main/java/org/commonmark/renderer/markdown/MarkdownRenderer.java
index edef645a4..d31a261da 100644
--- a/commonmark/src/main/java/org/commonmark/renderer/markdown/MarkdownRenderer.java
+++ b/commonmark/src/main/java/org/commonmark/renderer/markdown/MarkdownRenderer.java
@@ -44,7 +44,7 @@ public NodeRenderer create(MarkdownNodeRendererContext context) {
 
                     @Override
                     public Set<Character> getSpecialCharacters() {
-                        return Set.of();
+                        return Collections.emptySet();
                     }
                 });
     }
diff --git a/commonmark/src/main/java/org/commonmark/renderer/text/CoreTextContentNodeRenderer.java b/commonmark/src/main/java/org/commonmark/renderer/text/CoreTextContentNodeRenderer.java
index 22718d088..a20eac7c1 100644
--- a/commonmark/src/main/java/org/commonmark/renderer/text/CoreTextContentNodeRenderer.java
+++ b/commonmark/src/main/java/org/commonmark/renderer/text/CoreTextContentNodeRenderer.java
@@ -1,5 +1,8 @@
 package org.commonmark.renderer.text;
 
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashSet;
 import java.util.Set;
 import org.commonmark.node.*;
 import org.commonmark.renderer.NodeRenderer;
@@ -21,27 +24,29 @@ public CoreTextContentNodeRenderer(TextContentNodeRendererContext context) {
 
     @Override
     public Set<Class<? extends Node>> getNodeTypes() {
-        return Set.of(
-                Document.class,
-                Heading.class,
-                Paragraph.class,
-                BlockQuote.class,
-                BulletList.class,
-                FencedCodeBlock.class,
-                HtmlBlock.class,
-                ThematicBreak.class,
-                IndentedCodeBlock.class,
-                Link.class,
-                ListItem.class,
-                OrderedList.class,
-                Image.class,
-                Emphasis.class,
-                StrongEmphasis.class,
-                Text.class,
-                Code.class,
-                HtmlInline.class,
-                SoftLineBreak.class,
-                HardLineBreak.class);
+        return Collections.unmodifiableSet(
+                new HashSet<>(
+                        Arrays.asList(
+                                Document.class,
+                                Heading.class,
+                                Paragraph.class,
+                                BlockQuote.class,
+                                BulletList.class,
+                                FencedCodeBlock.class,
+                                HtmlBlock.class,
+                                ThematicBreak.class,
+                                IndentedCodeBlock.class,
+                                Link.class,
+                                ListItem.class,
+                                OrderedList.class,
+                                Image.class,
+                                Emphasis.class,
+                                StrongEmphasis.class,
+                                Text.class,
+                                Code.class,
+                                HtmlInline.class,
+                                SoftLineBreak.class,
+                                HardLineBreak.class)));
     }
 
     @Override