Check that a rune exists and is enabled
(active-runep '(:rewrite left-to-right))
(active-runep rune &optional strict)
where rune has the shape of a rune. This macro expands to an
expression using the variables ens and state, and returns
non-nil when the given rune exists and is enabled (according to
the given ``enabled structure,'' ens, and the current logical world of the given state). See theory-invariant for how this
macro can be of use.
When the optional argument is nil or is omitted, then although the
argument is required to have the shape of a rune, it need not be a
rune. For example, if there is no rewrite rule named left-to-right, then
(active-runep '(:rewrite left-to-right)) will simply return nil. If
instead you'd like this call to cause an error, use a non-nil optional
argument or, equivalently, use active-or-non-runep.