picture-tab-chars

picture-tab-chars is a variable defined in `picture.el'.
Its value is

"!-~"

Documentation:
A character set which controls behavior of commands.
M-x picture-set-tab-stops and M-x picture-tab-search.
The syntax for this variable is like the syntax used inside of `[...]'
in a regular expression--but without the `[' and the `]'.
It is NOT a regular expression, any regexp special characters will be quoted.
It defines a set of "interesting characters" to look for when setting
(or searching for) tab stops, initially "!-~" (all printing characters).
For example, suppose that you are editing a table which is formatted thus:
| foo | bar + baz | 23 *
| bubbles | and + etc | 97 *
and that `picture-tab-chars' is "|+*". Then invoking
M-x picture-set-tab-stops on either of the previous lines would result
in the following tab stops
: : : :
Another example - "A-Za-z0-9" would produce the tab stops
: : : :

Note that if you want the character `-' to be in the set, it must be
included in a range or else appear in a context where it cannot be
taken for indicating a range (e.g. "-A-Z" declares the set to be the
letters `A' through `Z' and the character `-'). If you want the
character `\' in the set it must be preceded by itself: "\\".

The command M-x picture-tab-search is defined to move beneath (or to) a
character belonging to this set independent of the tab stops list.

You can customize this variable.