This is a Brackets extension that converts the case of your selected text (lower case or upper case).
Install via the Extension Manager.
Highlight the text you want to convert and open the context menu by right clicking in the editor and selecting To Lower Case or To Upper Case ... or just use the following keyboard shortcuts:
Ctrl-Alt-Shift-L: Convert selected text to lower case
Ctrl-Alt-Shift-U: Convert selected text to upper case