Why does `.,.+[count]` appear in command box when typing [count+1] before :

Question

For example if in normal mode 4: is pressed, in the command line there will be :.,.+3. What does this mean and what is it used for?

Answer 1

This is a line range (see :h :range). "The dot" means the current line. So it's the current line and the next three ones.

The operation to perform over this line range, of course, depends on the command you type in the command-line.

So 4: is just a handy "shortcut" to input line range.