I have to replace a lot of variables `s1.size()` with `wa`, and replace `s2.size()` with `wb` accordingly. I have made next substitution request:
```vimscript
:'<,'>s/\vs([1|2])\.size\(\)/w\={"1":"a","2":"b"}[submatch(1)]/g
```
But it wont work. Also, if I remove that **w** from replacement field,
```vimscript
:'<,'>s/\vs([1|2])\.size\(\)/\={"1":"a","2":"b"}[submatch(1)]/g
```
it does almost what I want but of course it will replace just `s1.size()` with `a` and `s2.size()` with `b` without **w**.

How to put the vim script evaluation command `\=` and some text together in replacement field of substitute command?

I could not find help about `\=` with `:help`, if you know, please provide me a correct prompt to get vim help about `\=` command.