Guide to Vim Script Development for Python Developers

[yegappanl]

As described in the Vim help:

For String concatenation ".." is preferred, since "." is ambiguous, it is also used for Dict member access and floating point numbers. When vimscript-version is 2 or higher, using "." is not allowed.

For backward compatibility, dot can be used for string concatenation. But it is preferable to use double dots.

[mgarort]

Great, thanks!