Two kinds of tab-like action are provided in Picture mode. Use M-TAB (picture-tab-search ) for context-based tabbing. With no argument, it moves to a point underneath the next ``interesting'' character that follows whitespace in the previous nonblank line. ``Next'' here means ``appearing at a horizontal position greater than the one point starts out at.'' With an argument, as in C-u M-TAB, this command moves to the next such interesting character in the current line. M-TAB does not change the text; it only moves point. ``Interesting'' characters are defined by the variable picture-tab-chars , which should define a set of characters. The syntax for this variable is like the syntax used inside of `[...]' in a regular expression---but without the `[' and the `]'. Its default value is "!-~" .
TAB itself runs picture-tab , which operates based on the current tab stop settings; it is the Picture mode equivalent of tab-to-tab-stop . Normally it just moves point, but with a numeric argument it clears the text that it moves over.
The context-based and tab-stop-based forms of tabbing are brought together by the command C-c TAB, picture-set-tab-stops . This command sets the tab stops to the positions which M-TAB would consider significant in the current line. The use of this command, together with TAB, can get the effect of context-based tabbing. But M-TAB is more convenient in the cases where it is sufficient.