help-default-arg-highlight

[Glenn Morris]

The new help-default-arg-highlight is broken for me: now arguments are
not highlighted at all.

My display is capable of showing italics, hence
(display-supports-face-attributes-p '(:slant italic)) returns non-nil.
The font I use for the `default' face, however, does not have an
italic form. Therefore trying to make something italic through text
properties has no effect. I use a different font for the `italic'
face.

When this feature was being discussed on emacs-devel, it was
predicted that this would happen.