lmoustache/rmoustache as stretchy delimiters

Dear all,

It seems that lmoustache/rmoustache have been used as MathML stretchy operators for a long time. For example, itex2MML provides the \lmoustache & \rmoustache commands to generate these delimiters:

https://golem.ph.utexas.edu/~distler/blog/itex2MMLcommands.html#itex2MMLDelim

and Gecko has entries for U+23B0 and U+23B1:

https://dxr.mozilla.org/mozilla-central/source/layout/mathml/mathfont.properties?offset=300#1137

However, the MathML Operator dictionary does not contain any mention of lmoustache/rmoustache:

http://www.w3.org/TR/MathML3/appendixc.html

Should they be added to the official MathML dictionary or are they excluded on purpose?

Frédéric