It'd be great to see Brackets add to the provided HTML tags and attributes code hints such as the following:
HTML5 Tags
*Picture (Responsive Images)
*Template (Web Components)
HTML5 Attributes
*Autocorrect
*Autocapitalize
*Inputmode
*Itemscope, Itemtype, Itemprop (Schema.org)
HTML5 Attribute Options
*Audio ("buffered", "played")
*Autocomplete ("billing", "cc-name", "cc-number", "cc-css", "cc-exp-month", "cc-exp-year", "cc-type", "country", "email", "name", "postal-code", "region", "shipping", "street-address", "tel", "url")
*Img ("srcset")
*Input ("autocorrect")
*Link/rel ("import")
*Meta/name ("format-detection", "robots", "viewport")
*Textarea ("Autocorrect", "Autocapitalize")
*Video ("buffered", "crossorigin")
For the time being I have created a Brackets Extension which adds all of the above (along with some HTML 4 tags which many developers find useful) which is available now via the Brackets Extensions Manager.