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Contexts
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How to use a context
- Identify context.
- Determine whether to fetch resource based on CSP directives and type hint, if any.
- Fetch resource.
- Set no-sniff flag on resource (based on URL), if necessary.
- Handle resource.
- Sniff resource.
- Process and display resource or prompt to download resource, as appropriate.
Context types
| Context | Definition | Used in HTML? | Used in CSS? | Scriptable? | CSP Directive | Type Hint | Sniffing Algorithm |
|---|---|---|---|---|---|---|---|
| browsing (navigate) | HTML | Yes | No? | Yes | — | MIME type sniffing algorithm | |
| nested browsing (navigate) | 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"
|
Context triggers
| Context | HTML Triggers | CSS Triggers | Other Triggers |
|---|---|---|---|
| browsing | |||
| nested browsing | <iframe>, <object> (sometimes), <frame>
|
||
| connection | EventSource, WebSocket, XMLHttpRequest | ||
| image | <img>, <link rel=icon>, <input type=image>, <object> (sometimes)
|
background-image
|
|
| audio/video | <audio>, <video>
|
||
| plugin | <embed>, <object> (sometimes)
|
||
| style | <link rel=stylesheet>
|
@import?
|
|
| script | <script src>
|
||
| font | — | @font-face
|
FontFace#load(), FontFaceSet#load() |
| text track | <track>
|
— | |
| cache manifest | <html manifest>
|
— |
Issues
- What about SVG?
- What about XSLT?
- document.load()? (Seems similar enough to connect-src.)
- What about CSS masks?
- What about CSS shapes?