the expression register
The expression register (=) can be used to evaluate expressions, like 2+3. If this register is used while in Insert mode (<C-r>=), the results of the expression will be inserted after the expression is evaluated.
The expression register (=) can be used to evaluate expressions, like 2+3. If this register is used while in Insert mode (<C-r>=), the results of the expression will be inserted after the expression is evaluated.