When file extension is .xsl everything is good, but with .xslt it falls back to default: html, so I cannot expand XSLT code.
I believe it does not look at file extension, because for whatever file, if you choose CSS as syntax highlight, you can expand CSS, eg: 'va' expands to 'vertical-align: top;'; if you choose any other syntax highlight, 'va' expands to ''.
The problem is I am already using XML syntax highlight for both .xsl and .xslt . I tried to edit the config file C:\Program Files (x86)\Notepad++\plugins\EmmetNPP\emmet\snippets.json but there was just no difference.