Your comments

Here another one.

After matching the scope at the cursor, white keyboard appears over the dark one

This is my testing sample:

"string": "${3:test}",
"append": "${1:sample}: ${1/.*/\\u/g}"
The idea is to make the value entered in the first line uppercase, but it just returns the cursor to beginning of line

Can you provide a working sample for "transformations"?

i mean "transformations" for code compltion, something like this {"string": "scale2", "append": "(${1:0.5}${1/(.+)/(?1:, )/}${2:0.5});"},