Manual:$wgDebugComments

Details
If on, some debug items may appear in comments in the HTML output.

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As of MediaWiki-1.8.2,   writes one HTML comment near the beginning of the page body with the template:



Debug text passed to function   is included in the text of this debug comment unless an optional second parameter (named  ) is passed to   which evaluates as true.

Use on production sites is not recommended.

Debug comments reveal information in page views which could potentially expose security risks.