Manual:$wgDocType

Output: $wgDocType
The doc type to use in the <!DOCTYPE> declaration.
Introduced in version:Before 1.1.0
Removed in version:1.22.0 (Gerrit change 63106; git #97caae59)
Allowed values:(string)
Default value:'-//W3C//DTD XHTML 1.0 Transitional//EN' (1.3-1.21)
'-//W3C//DTD HTML 4.01 Transitional//EN' (pre1.1 - 1.2)

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The doc type to use in the <!DOCTYPE> declaration.

This may not be taken into consideration if $wgHtml5 is set to true.