def std_substring(args, ctxt):
(s, start) = argver(args, [core.string, core.number],
reqargs=2, maxargs=3)
start = int(start) - 1 # XPath is 1-based
if start < 0: start = 0
if (len(args)>2):
span = int(core.number(args[2]))
if span < 0: span = 0
return s[start:start+span]
return s[start:]
def std_number(args, ctxt):
"convert argument to a number"
argver(args, [core.number], reqargs=1, maxargs=1)
return core.number(args[0])
