What language or framework commonly uses tags like ""

You will see it in the source code of many web sites as follows:

<!--ls:begin[stylesheet]-->
<!--ls:end[stylesheet]-->

It appears to be some method of moving pieces defined in the body of some templating engine to the <head> of the the document (or wherever makes sense).

For example, see the HTML for this site: view-source:http://www.theaa.com/

Those tags are produced by LiveSite, which is part of TeamSite enterprise CMS now owned by HP. Back in the days the company that found it was called Interwoven, then bought by Autonomy and now days it's HP.

http://www.autonomy.com/products/teamsite