You can remove or add a level of indentation to the selected lines. To change the indentation level:
The selection will be expanded to consist of complete lines, and a tab character will be removed from or added to the start of each selected line.
AppleScript will perform its own indentation when the script is compiled, which may alter the number of tab characters at the start of a line (except inside a multiline string literal).
See also on Show Invisibles, Show Spaces, and Show Tab Stops.