internal override int contextLength()
{
if (op == RegOp.context) throw new StringInterpretException("multiple context operators");
else
{
int lLen = lKid.contextLength();
int rLen = rKid.contextLength();
if (lLen <= 0 || rLen <= 0) return 0;
else if (op == RegOp.concat) return lLen + rLen;
else if (lLen == rLen) return lLen;
else return 0;
}
}