1. Let spellcheck be sensible to the lang attribute of HTML and XHTML as well as of the xml:lang attribute of XML. 
• E.g. when using an English spell checker, then, when faced with <p>Petite</div>, do not perform English spell check inside that element.
  
• If present in HTML or XHTML, the @lang attribute should take presedence - though perhaps some may want to fiddle with the presendence.
• Spellcheck could either be fully multilingual (thus allow checking of many languages at once, if the document includes more than one langauge). But as long as spell checking is monolingual, it should behave as described in point 1.
2. Also make it possible to declare that no attributes should be checked, except those which one allows it for. (Such as @title and @alt in XHTMl and HTML elements.)
   
3. Textile and MarkDown etc may also support language declaration, and it would be nice to implement that too.
4. To save you the hazzle from adding support for all the 8000+ registered language tags, I guess it would be fine if one could declare, e.g. in the preferences that lang="fr" refers to a French dictionary, while lang="nn" refers to a Norwegian Nynorsk dictionary — etc.

Title says it all.

Save which code I have collapsed. It doesn't when I collapse code and open Sublime again.

For example, in a PHP file, there can be JavaScript, CSS, and HTML, so it would be really great if different parts of a file could be set as a different language for syntax highlighting and for other features.

I know that in for example Monokai color scheme there is: activeGuide key, but setting a new inactiveGuide does nothing.