Position of a pattern-matched part of an expression

What you have

A pattern, with certain part of it labeled

As an example — Label: wally
```
pattern = h : HoldPattern@f[x, __, 3[5], wally_, y]
```

An expression that matches a pattern such as:
```
expr = f[x, 9, v, h[v], 3[5], v, y]
```

What I want

The position of the part of the expression expr that matched the label wally.

In the above example, that would be

gimmeWhattaWanna[expr, pattern, wally]
(* {{6}} *)

Note

If the labeled pattern is a sequence such as wally__, either finding the position of the first, or the first and last, are acceptable. If the labeled pattern is repeated such as in f[wally_, 2, wally_], then a list of the positions seems the most natural solution. However, a solution that limits itself to non-repeated labels, or even non-sequence ones is useful.

Comments

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