Execute the function. The function must return
a valid object.
String s1 = m_arg0.execute(xctxt).str();
String s2 = m_arg1.execute(xctxt).str();
// Add this check for JDK consistency for empty strings.
if (s1.length() == 0 && s2.length() == 0)
return XBoolean.S_TRUE;
int index = s1.indexOf(s2);
return (index > -1) ? XBoolean.S_TRUE : XBoolean.S_FALSE;