'Trim `length` characters off the beginning of each item, in-place,
from index `start` to `end`.  No whitespace-checking is done on the
trimmed text.  Does not affect slice parent.'

def trim_left(self, length, start=0, end=sys.maxint):

    self.data[start:end] = [line[length:] for line in self.data[start:end]]
