Snippet Text Transform

[touhid_rahman]

I know how to change text to uppercase in another place using this code:
${1/./\u$0/g}

But if I want to type type any case and want to change that to uppercase in the typing place (not another place); what will be the code?
Such as,
${1:header} allows me to just type but dont change text case. I want to type and change text case in the place I am typing; I hope it makes sense.

[kingkeith]

snippet substitutions can currently only take effect against a placeholder where you are not typing (as per the answer you have already received, you will have to find a different solution for now