dropAnchor on caps-height or x-height?

[vinuel]

dropAnchor has some really helpful alignment expressions! I wonder if it is possible to place anchors at the cap height or x-height.

'Top' places the anchor at the highest point of a glyph, this results in different anchor positions for glyphs with overshoot,
but anchors should all be at the same height in a font and it would be great to do so by an expression.

[vinuel]

In my case I use a workaround now with moveAnchor to shift the 'top' anchor to the caps height or x-height, but I think having an expression for this would be a nice enhancement!