bodyless tags - word syntax

[12Me21]

abc \sup def ghi

• syntax for the word argument
• does the space get eaten?

[y-ack]

word/line eating behavior discussed extensively
[2022 04 02] comments/31843?ids=787445-787780
[2022 04 04} comments/31843?ids=790060-790119

the conclusion maybe? was

the [space] is only eaten if it is NECESSARY to form a word boundary

\tag abc def sshould have no space
but \tag abc \tag abc should have 1 (since \tag abc\tag abc is valid)