[css-masking] definition of 'masking box'

https://drafts.fxtf.org/css-masking-1/#valdef-mask-clip-margin-box says:

margin-box
    The painted content is restricted to (clipped to) the masking box. 

Does it mean to say "margin box" rather than "masking box"?  If not,
"masking box" needs to be defined somewhere.  This is the only
occurrence of the term in the spec.

-David

-- 
𝄞   L. David Baron                         http://dbaron.org/   𝄂
𝄢   Mozilla                          https://www.mozilla.org/   𝄂
             Before I built a wall I'd ask to know
             What I was walling in or walling out,
             And to whom I was like to give offense.
               - Robert Frost, Mending Wall (1914)