Why do some Vim mappings include after a colon?

Question

I'm trying to figure out the syntax of the mapping commands, like `onoremap`, in vim. Specially, I am confused over this line in the manual, regarding the use of ``: The CTRL-U (``) is used to remove the range that Vim may insert. Can someone explain this?

Accepted Answer

That isn't part of the syntax for the `onoremap` command, that is explaining what a particular mapping does. That mapping is: ``` onoremap F :normal! 0f(hviw ``` So, when the `F` key is used while an operator is pending vim will replace that with the bits in the next argument to the `onoremap` command. That starts with a `:` to begin an `ex` mode command. If there is a visual selection when the mapping is used, vim will automatically insert the range `'<,'>` so that the following `ex` command will apply to the visual selection, leaving the command line looking like: ``` :'<,'> ``` The `` in the mapping tells vim that after the `:` is entered the Control+U combination should be used to clear the command line, eliminating the automatically inserted range leaving the command line looking like: ``` : ``` Then the remainder of the mapping is used. You can see this for yourself by using V to begin a line-wise visual selection, then : to start entering a command. The range will show up, you can then use Control+U to clear it just as the example mapping does. The portion of vim help that contains that mapping explains the remainder of it.

Why do some Vim mappings include <C-U> after a colon?

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