Make your site LibreJS-friendly and HTML5-valid with rel=jslicense attribute
The rel="jslicense" attribute allows tools, such as GNU LibreJS, to know where to find the labels page to determine if each JS file being served is free software, and if it is, then to allow your browser to download and run that program.
Unfortunately, when we first published our web labels recommendation, one problem web developers encountered was the fact that rel="jslicense" attribute was not considered "valid" HTML5, and so tools such as W3C's Markup Validation Service would return an error stating that the rel="jslicense" tag was invalid attribute. However, earlier this month, we were able to get rel="jslicense" to become a rel value that is considered valid HTML5.
To get rel="jslicense" recognized as a valid HTML5 link type, we needed to get it listed on the existing-rel-values page of the Microformats.org wiki. Specifically, the W3C's HTML5 specification states that link types defined as extensions in the Microformats.org wiki page with the status "proposed" or "ratified" may be used with the rel attribute on <link>, <a>, and <area> tags. So, in 2014, we submitted our "jslicense" rel-value for review on Microformats.org, and then after some conversations with Microformats.org administrators and showing that various sites were actually making use of "jslicense" rel-value, the good folks at Microformats.org listed "jslicense" as a valid (i.e. "proposed") HTML5 link type extension.
Special thanks to Tantek Çelik of Microformats.org for taking the time to give us feedback on our proposal and for ultimately adding it as a proposed value.