Dummy variable:
@example
a = 3
  @result{} a = 3
@end example

The regex for SKIP_IF argument should not cross newlines!  First, note its ok
to have syntax errors in skipped tests:
@example
@c doctest: +SKIP
a = 5*(5+1))
  @result{} b = 0
@end example

But next we have a syntax error, combined with SKIP_IF code.  The IF code
should not glob the @code{a = } bit: might result in a syntax error if it did.
@example
@c doctest: +SKIP_IF(6 + 0*now () >= 0)
a = 3*(4+1))
  @result{} a = 15
@end example

As above, but two SKIP_IF's
@example
@c doctest: +SKIP_IF(6 + 0*now () >= 0)
@c doctest: +SKIP_IF(7 + 0*now () >= 0)
a = 3*(4+1))
  @result{} a = 15
@end example


Finally, a is still 3
@example
a
  @result{} a = 3
@end example
