The number of spaces used for the left margin. The value provided is silently converted to a positive integer value.

                           columns
<-------------------------------------------------------------->
<-----------><------><---------------------------><------------>
 LEFT MARGIN  indent  text is formatted into here  right margin

Source Code

# File action_mailer/vendor/text-format-0.6.3/text/format.rb, line 214
def left_margin=(left)
  @left_margin = posint(left)
end