[TxMt] Placeholders within transformations in snippets

I have a suspicion this can’t be done, but perhaps I’ve just missed something.

I’m trying to write a snippet to insert operator declarations in Swift. The basic syntax is

(postfix|infix|prefix) operator <name> { }

But, if we are declaring an infix operator, we may also add

precedence <level> associativity (left|right|none)

inside the curly brackets.

This is what I’ve got, based on the example at the end of section 6.8 in the manual.

${1|infix,prefix,postfix|} operator ${2:name} { ${1/(infix)|prefix|postfix/${1:+\n\tassociativity ${3|left,right, none|}\n\tprecedence${4:level}\n}/}}

As you can see if you can read that lot, I’m trying to use $3 and $4 as placeholders within the conditional insertion.

It doesn’t work of course. I assume this is because in that context $3 and $4 refer to captures from the regular expression. Is that so? Is there any way round this?

Thanks to anyone who can help

Nigel Chapman