If UserValue names are too long, controls do not work correctly

[Sciss]

There is no provision for ensuring control names are short, resulting in errors, for example in the following case of UserValue keys:

"temperature thresh low  [°]"  // 27 -- broken
"temp thresh low  [°]" // 20 -- ok

We need to use something akin to the abbreviate method used for the synth def names.