[css-masking] Editorial nits on lists or not

Dirk,

It looks like CSS Masking got some copy-and-paste errors from matching
background-* properties. In background-position, you have a list of
<position> values, but in mask-position there's only one <position> value.
The mask-position property table gets confused about this, though.

Computed Value should not say "A list, each item" (the same problem is in
mask-repeat)

Animatable should not say "repeatable list of simple list" (the same
problem is in mask-size)


And the mask-position Percentages item says to see the text, but should
probably have a link to the text in the background spec.

Thanks,

Alan