[TASK] Provide description for "canonical_url" field

- Short description of the function
- Hint that TYPO3 sets default values
- Hint that setting a value will remove the page from the XML sitemap

The behaviour can be changed by the integrator/developer of cause, but
the label can be changed via TCA override in that case.

Resolves: #101841
Releases: main, 12.4
Change-Id: Ic74e02fa4de4aa0a6708123caa596271b7b27561
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/80899


Tested-by: core-ci <typo3@b13.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>

typo3/sysext/seo/Configuration/TCA/Overrides/pages.php

@@ -146,6 +146,7 @@ $tca = [
         'canonical_link' => [
             'exclude' => true,
             'label' => 'LLL:EXT:seo/Resources/Private/Language/locallang_tca.xlf:pages.canonical_link',
+            'description' => 'LLL:EXT:seo/Resources/Private/Language/locallang_tca.xlf:pages.canonical_link.description',
             'displayCond' => 'FIELD:no_index:=:0',
             'config' => [
                 'type' => 'link',

typo3/sysext/seo/Resources/Private/Language/locallang_tca.xlf

@@ -67,6 +67,9 @@
 			<trans-unit id="pages.canonical_link" resname="pages.canonical_link">
 				<source>Canonical link</source>
 			</trans-unit>
+			<trans-unit id="pages.canonical_link.description" resname="pages.canonical_link.description">
+				<source>A canonical URL is the URL of a page that search engines are advised to choose as the most representative from a set of duplicate pages. Often called deduplication, this process helps search engines show only one version of the otherwise duplicate content in its search results. TYPO3 automatically sets this to the most likely URL of the page if not set explicitly - which is most likely the URL of the page itself. If set here, the page will be removed from the XML sitemap.</source>
+			</trans-unit>
 			<trans-unit id="pages.tabs.socialmedia" resname="pages.tabs.socialmedia">
 				<source>Social media</source>
 			</trans-unit>