bug#74: Bug#74: defcustom keyword :custom-show isn't documented

[Glenn Morris]

reassign 74 emacs
stop

Reiner Steib wrote:

> Neither the doc string of `defcustom', nor the manual explains it.

It seems that it (:custom-show) is supposed to make the variable value
field be hidden by default when it is created. In other words, make the
custom buffer look like you have clicked the "Hide the value of this
option" button.

The idea is that when a variable has a complex value, it should be
hidden by default, to avoid cluttering up the display.

However, AFAICS it doesn't work (in Emacs 21, 22, or 23).
custom-variable-value-create only uses custom-show when a variable has a
nil :custom-state. Since variables are created with state 'unknown, it
never does anything.

Making the obvious change doesn't work (the variable is created hidden
ok, but can't be unhidden by clicking the relevant button).

Given that it seems never to have worked, I'm not sure it's worth
bothering trying to fix it. It's only used in gnus-art (and cus-edit
tries to apply it to long editable-fields).