[css-text-decor-4] Default end value of text-decoration-trim when a single length is specified?

[cdoublev]

Can you please clarify what is the value of the end point when a single length is specified?

Name: text-decoration-trim
Value: <length>{1,2} | auto

0 seems a sensible option. The inverse of the start point may be more intuitive, eg. -1em when the start point is 1em. Or auto, but the syntax does not allow to explicitly declare it.