Docs: Link to the "Conditional Tags" article in the Theme Developer Handbook from the descriptions for a variety of core conditional tag functions.

These notations largely serve to direct consumers (of both the source and the parsed code reference) to extended information on individual and related conditional tags throughout WordPress. The changeset also standardizes corresponding DocBlock summaries to use third-person singular verbs.

Notations been added for the following functions:

* comments_open()
* email exists()
* has_excerpt()
* has_post_thumbnail()
* has_tag()
* in_category()
* in_the_loop()
* is_404()
* is_active_sidebar()
* is_active_widget()
* is_admin()
* is_admin_bar_showing()
* is_archive()
* is_attachment()
* is_author()
* is_blog_installed()
* is_category()
* is_comments_popup()
* is_date()
* is_day()
* is_dynamic_sidebar()
* is_feed()
* is_front_page()
* is_home()
* is_local_attachment()
* is_main_query
* is_month()
* is_multi_author
* is_new_day()
* is_page()
* is_page_template()
* is_paged()
* is_plugin_active()
* is_plugin_active_for_network()
* is_plugin_inactive()
* is_plugin_page()
* is_post_type_archive()
* is_preview()
* is_rtl()
* is_search()
* is_single()
* is_singular()
* is_sticky()
* is_tag()
* is_tax()
* is_taxonomy_hierarchical()
* is_time()
* is_trackback()
* is_user_logged_in()
* is_year()
* pings_open()
* post_type_exists()
* taxonomy_exists()
* term_exists()
* username exists()
* wp_attachment_is_image()
* wp_script_is()

Props janalwin.
Fixes #43254.

Built from https://develop.svn.wordpress.org/trunk@42710


git-svn-id: http://core.svn.wordpress.org/trunk@42538 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/plugin.php

@@ -457,13 +457,17 @@ function _get_dropins() {
 }
 
 /**
- * Check whether a plugin is active.
+ * Determines whether a plugin is active.
  *
  * Only plugins installed in the plugins/ folder can be active.
  *
  * Plugins in the mu-plugins/ folder can't be "activated," so this function will
  * return false for those plugins.
- *
+ * 
+ * For more information on this and similar theme functions, check out
+ * the {@link https://developer.wordpress.org/themes/basics/conditional-tags/ 
+ * Conditional Tags} article in the Theme Developer Handbook.
+ * 
  * @since 2.5.0
  *
  * @param string $plugin Path to the main plugin file from plugins directory.
@@ -474,10 +478,14 @@ function is_plugin_active( $plugin ) {
 }
 
 /**
- * Check whether the plugin is inactive.
+ * Determines whether the plugin is inactive.
  *
  * Reverse of is_plugin_active(). Used as a callback.
- *
+ * 
+ * For more information on this and similar theme functions, check out
+ * the {@link https://developer.wordpress.org/themes/basics/conditional-tags/ 
+ * Conditional Tags} article in the Theme Developer Handbook.
+ * 
  * @since 3.1.0
  * @see is_plugin_active()
  *
@@ -489,17 +497,21 @@ function is_plugin_inactive( $plugin ) {
 }
 
 /**
- * Check whether the plugin is active for the entire network.
+ * Determines whether the plugin is active for the entire network.
  *
  * Only plugins installed in the plugins/ folder can be active.
  *
  * Plugins in the mu-plugins/ folder can't be "activated," so this function will
  * return false for those plugins.
- *
+ * 
+ * For more information on this and similar theme functions, check out
+ * the {@link https://developer.wordpress.org/themes/basics/conditional-tags/ 
+ * Conditional Tags} article in the Theme Developer Handbook.
+ * 
  * @since 3.0.0
  *
  * @param string $plugin Path to the main plugin file from plugins directory.
- * @return bool True, if active for the network, otherwise false.
+ * @return bool True if active for the network, otherwise false.
  */
 function is_plugin_active_for_network( $plugin ) {
 	if ( ! is_multisite() ) {