Studio uses different editors to modify files. For example, Studio
uses the TiApp editor to modify the tiapp.xml
file, and the Alloy XML View editor to modify all other XML files. You
can open up multiple editor, but only one can be active. Each file
type (or file) can be associated with different editors or an external
program within Studio.
Depending on the Editor, Studio may show warning and errors. You can also add breakpoints for debugging in certain editors.
If you do not want to open the file in its default editor, in the Project Explorer view, right-click the file, select Open With..., then choose an Editor to open the file or Other... to select from a list of Editors.