How to convert a selection to lowercase or uppercase in Sublime Text

In the current version of Sublime Text 2 (Build: 2139), you can set the syntax for all files of a certain file extension using an option in the menu bar. Open a file with the extension you want to set a default for and navigate through the following menus: View -> Syntax -> Open all with current extension as... ->[your syntax choice].

Updated 2012-06-28: Recent builds of Sublime Text 2 (at least since Build 2181) have allowed the syntax to be set by clicking the current syntax type in the lower right corner of the window. This will open the syntax selection menu with the option to Open all with current extension as... at the top of the menu.

Updated 2016-04-19: As of now, this also works for Sublime Text 3.

You don't need any plugins to do this. Just select all lines (CTRL+A) and then from the menu select Edit → Line → Reindent. This will work if your file is saved with an extension that contains HTML like .html or .php.

If you do this often, you may find this key mapping useful:

{ "keys": ["ctrl+shift+r"], "command": "reindent" , "args": { "single_line": false } }

If your file is not saved (e.g. you just pasted in a snippet to a new window), you can manually set the language for indentation by selecting the menu View → Syntax → language of choice before selecting the reindent option.