Return indent-info for this line.
This is a list. nil means the line is to be left as is.
Otherwise it contains one or more of the following sublists:
(t NUMBER) NUMBER is the base location in the buffer that indentation is
relative to. If present, this is always the first of the
sublists. The indentation of the line in question is
derived from the indentation of this point, possibly
modified by subsequent sublists.
(+ VAR)
(- VAR) Get the value of variable VAR and add to or subtract from
the indentation calculated so far.
(= VAR) Get the value of variable VAR and *replace* the
indentation with its value. This only occurs for
special variables such as `sh-indent-comment'.
STRING This is ignored for the purposes of calculating
indentation, it is printed in certain cases to help show
what the indentation is based on.