When setting "formatOtherKeys" resource to 1 in xterm, 'CSI u' format is
used for non-standard keycodes.  This is also how mintty support
"modifyOtherKeys" by default.

But in term/xterm.el, only 'CSI 27" format is supported.

I think it is worth supporting "CSI u" format control sequences.
What do you think of adding them to teerm/xterm.el?  or anyone can do it?

/Victor