You can comment and uncomment lines and blocks of code using &shortcut:CommentByLineComment; and &shortcut:CommentByBlockComment;.
&shortcut:CommentByLineComment; comments or uncomments the current line or selected block with single line comments (#...).
&shortcut:CommentByBlockComment; encloses the selected block in a begin / end pair (=begin / ... =end).
To uncomment a commented block press &shortcut:CommentByBlockComment; anywhere inside it.