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Preserving Tabstop Alignment
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   The lines of text in some of the `diff' output formats are preceded
by one or two characters that indicate whether the text is inserted,
deleted, or changed.  The addition of those characters can cause tabs to
move to the next tabstop, throwing off the alignment of columns in the
line.  GNU `diff' provides two ways to make tab-aligned columns line up
correctly.

   The first way is to have `diff' convert all tabs into the correct
number of spaces before outputting them; select this method with the
`-t' or `--expand-tabs' option.  `diff' assumes that tabstops are set
every 8 columns.  To use this form of output with `patch', you must
give `patch' the `-l' or `--ignore-white-space' option (Note: Changed
White Space, for more information).

   The other method for making tabs line up correctly is to add a tab
character instead of a space after the indicator character at the
beginning of the line.  This ensures that all following tab characters
are in the same position relative to tabstops that they were in the
original files, so that the output is aligned correctly.  Its
disadvantage is that it can make long lines too long to fit on one line
of the screen or the paper.  It also does not work with the unified
output format, which does not have a space character after the change
type indicator character.  Select this method with the `-T' or
`--initial-tab' option.