In all HTMLs and XHTMLs before HTML5 and in XHTML5 it is required to be upper case. As the lexer that highlights html is not sensitive to the version it can't change its habits based on the version.
The lexer itself comes from the [Scintilla](http://www.scintilla.org/) project so you would need to ask for it there to make it vary by version. -- You are receiving this because you are subscribed to this thread. Reply to this email directly or view it on GitHub: https://github.com/geany/geany/issues/1489#issuecomment-298947778
