Contexts

Context types

Context	Definition	Used in HTML?	Used in CSS?	Scriptable?	CSP Directive	Type Hint	Sniffing Algorithm
browsing	HTML	Yes	No?	Yes		—	MIME type sniffing algorithm
nested browsing	HTML	Yes	No?	Yes	frame-src
connection		Yes	No?	Yes?	connect-src
image		Yes	Yes	No	img-src		rules for sniffing images specifically
audio/video		Yes	No?	No	media-src		rules for sniffing audio and video specifically
plugin		Yes	No?	Yes?	object-src		rules for sniffing in a plugin context
style		Yes	Yes?	No	style-src	@type or "text/css"	rules for sniffing in a style context
script		Yes	No?	Yes?	script-src	@type or "text/javascript"	rules for sniffing in a script context
font		No	Yes	No	font-src	format()	rules for sniffing fonts specifically
text track		Yes	No	No		"text/vtt"
cache manifest		Yes	No	No		"text/cache-manifest"

How to use a context

1. Identify context.
2. Determine whether to fetch resource based on CSP directives and type hint, if any.
3. Set no-sniff flag on resource, if necessary.
4. Fetch resource.
5. Handle resource.
6. Sniff resource.
7. Process and display resource or prompt to download resource, as appropriate.