length can be defined in docInit but is not recognized in a length attribute like frame.x1

[joeUser555]

BUG/PROBLEM REPORT / FEATURE REQUEST

I don't know is it a bug report or a feature request.

What I did:

I defined a length in docInit:

    <docInit>
            <length id="l1" value="30mm"/>
    </docInit>

and I used it in a frame:

<frame id="XXX" showBoundary="0" x1="l1" y1="10mm" width="180mm" height="10mm"/>

What I expect to happen:

The l1 reference should be replaced by the length(30mm) defined in the docInit section.

What actually happened:

An exception is raised:
ValueError: The value 'l1' is not a valid measurement.

What version of Python and Zope/Addons I am using:

Python 3.10
Zope-Event 4.6

[regebro]

Length isn't implemented.