code: func checkWhitespace(a, b string) int {
  	i := 0
  	for ; i < len(a); i++ {
  		if a[i] != ' ' && a[i] != '\t' {
  			// a has run out of whitespace and b matched up to this point.  Return
  			// result.
  			return i
  		}
  		if i >= len(b) {
  			// We ran off the edge of b while a still has whitespace.  Return 0 as
  			// failure.
  			return 0
  		}
  		if a[i] != b[i] {
  			// a has whitespace but b does not.  Return 0 as failure.
  			return 0
  		}
  	}
  	// We ran off the end of a and b kept up
  	return i
  }
docs: // Check that b has at least the same whitespace prefix as a and returns the
  // amount of this whitespace, otherwise returns 0.  If a has no whitespace
  // prefix than return 0.