Currently WinSCP is using an odd syntax mixing of !?&... for its custom commands.
Its not readable, and cause mistakes even for me as a programmer ..
It will be too complicated to use and for commands which contain begin and end parts for example for:
tar -cz -f "!?&Archive Name:?archive.tgz!" !&
if I want to change "archive.tgz" to current selected file which is called from current syntax by ! it won't work as expected because its closing tag is same as tag for current file.
I hope at least begin and end tag characters should be at least different like <,> or [,] so when you I put a none block tag (without begin and end) like !(filename) to that container.. not mix with syntax of container pattern.