Question About Emoji Gender Encoding "Sign Format" vs. "Object Format"

[Scott Colby]

Hello,

I was recently looking at "Update on Emoji Gender and Skintone
Support" (https://www.unicode.org/L2/L2020/20196-gender-skintone-update.pdf)
and noticed a statement on page 6 that raised my curiosity:

> Note: we cannot use “sex symbols” to denote GI so we must employ
> objects

I attempted to track down this requirement, but have been unable
to do so.

The closest information I found was Technical Report #51, section
2.3.1 (https://www.unicode.org/reports/tr51/#gender-neutral):

> [H]uman-form emoji should normally be depicted in a gender-neutral
> way unless gender appearance is explicitly specified using an emoji
> ZWJ sequence in one of the ways shown in the following table.

The table then describes "Sign Format" (the one the note from the
first document says cannot be used) and "Object Format."

I'm guessing that TR#51 is descriptive of the current state and not
prescriptive for future encoding decisions. Is this correct?

Can someone point me to the official basis of the prohibition on
"Sign Format" for encoding of emojis with explicit genders? Was
this a technical decision or was it done for non-technical reasons?
Either way, what was the reasoning?

I attempted to find an address for Jennifer Daniel or the Emoji
Subcommittee (the authors of the document that piqued this question),
but was unable to do so. I hope this is the proper forum for this
question. If not, I would appreciate direction to the appropriate
one.

Thank you,
Scott Colby