substring

# File lib/rexml/functions.rb, line 231
    def Functions::substring( string, start, length=nil )
      ruby_string = string(string)
      ruby_length = if length.nil?
                      ruby_string.length.to_f
                    else
                      number(length)
                    end
      ruby_start = number(start)

      # Handle the special cases
      return '' if (
        ruby_length.nan? or
        ruby_start.nan? or
        ruby_start.infinite?
      )

      infinite_length = ruby_length.infinite? == 1
      ruby_length = ruby_string.length if infinite_length

      # Now, get the bounds.  The XPath bounds are 1..length; the ruby bounds
      # are 0..length.  Therefore, we have to offset the bounds by one.
      ruby_start = round(ruby_start) - 1
      ruby_length = round(ruby_length)

      if ruby_start < 0
       ruby_length += ruby_start unless infinite_length
       ruby_start = 0
      end
      return '' if ruby_length <= 0
      ruby_string[ruby_start,ruby_length]
    end