ORELSECop Conv.ORELSEC : (conv -> conv -> conv)Applies the first of two conversions that succeeds.
(c1 ORELSEC c2) ``t`` returns the result of applying the
conversion c1 to the term ``t`` if this
succeeds. Otherwise (c1 ORELSEC c2) ``t`` returns the
result of applying the conversion c2 to the term
``t``. If either conversion raises the
UNCHANGED exception when applied, this is passed on to
ORELSEC’s caller.
(c1 ORELSEC c2) ``t`` fails if both c1 and
c2 fail when applied to ``t``. (This refers to
failure other than by raising UNCHANGED).