introduce "See also" config

c.list

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!-- Copyright 2000-2024 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license. -->
+
+<!DOCTYPE categories SYSTEM "https://resources.jetbrains.com/writerside/1.0/categories.dtd">
+<categories>
+  <category id="related" name="Related topics" order="1"/>
+  <category id="external" name="External resources" order="2"/>
+</categories>

topics/tutorials/writing_tests_for_plugins/writing_tests_for_plugins.md

@@ -1,7 +1,7 @@
-<!-- Copyright 2000-2023 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license. -->
-
 # Testing a Custom Language Plugin
 
+<!-- Copyright 2000-2024 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license. -->
+
 <link-summary>Tutorial demonstrating how to develop tests for custom language plugin features.</link-summary>
 
 > Please see [](testing_plugins.md) for a general introduction.
@@ -26,3 +26,9 @@ As an example, the plugin implemented in the [Custom Language Support Tutorial](
 * [](commenter_test.md)
 * [](reference_test.md)
 * [](documentation_test.md)
+
+<seealso style="cards">
+    <category ref="related">
+    <a href="testing_plugins.md"/>
+    </category>
+</seealso>

writerside.cfg

@@ -14,5 +14,6 @@
     <vars src="v.list" />
     <vars src="v-releases.list" />
     <snippets dir="code_samples"/>
+    <categories src="c.list"/>
     <instance src="ijs.tree" keymaps-mode="none" id="intellij" web-path="/intellij/"/>
 </ihp>