TIP #256 Version 1.4: Implement Tabular and Wordprocessor Style Tabbing

This is not necessarily the current version of this TIP.

Abstract

There are two common style of tabbing in the computer world: that used for a regular table of information, and that used by a word-processor/text editor. This TIP proposes to add support for the latter to Tk's text widget.

Overview

Tk's text widget has historically only supported a tabular style of tabbing, where the n'th tab character is associated explicitly with the n'th tab stop (irrespective of whether that stop is to the left or right of the current x-position - if that stop is to the left then a single space is inserted as a fallback). A wordprocessor (or typewriter) has a different style in which a tab character is associated with the next tab stop to the right of the current x-position.

This TIP proposes to add wordprocessor-style tabbing to Tk's text widget.

Tk 8.4 only supports tabular tabbing (although this is not clearly documented at all). Tk 8.5 at present actually only supports wordprocessor style tabbing (and fixed a bunch of other bugs present in Tk 8.4's tab handling). This behaviour change was an inadvertent result of fixing bugs in the code without the correct behaviour being very clearly specified. Hence this TIP will restore the old behaviour (minus bugs) as the default, and add the option of the new wordprocessor style behaviour.

Proposal

A new -tabstyle configuration option will be added to the text widget, taking the values wordprocessor or tabular to specify the style of tabbing. The same option will also be added to tags in the text widget (which, as usual, will also allow an empty value for the configuration option). The default style of tabbing will be tabular for compatibility with Tk 8.4. Neither style name may be abbreviated.

Here's an example usage:

pack [text .t]
.t config -tab {0.5i 1.0i 1.5i 2.0i 2.5i 3.0i 3.5i 4.0i 4.5i}
.t insert end "a\tb\tc\tasdbcanasdasd\te\tf\tg\n"
.t insert end "a\tb\tc\tasdbcanasdasd\te\tf\tg\n"
.t insert end "a\tb\tc\tasdbcanasdasd\te\tf\tg\n"
.t insert end "a\tb\tc\tasdbcanasdasd\te\tf\tg\n"
.t insert end "a\tb\tc\tasdbcanasdasd\te\tf\tg\n"
.t insert end "a\tb\tc\tasdbcanasdasd\te\tf\tg\n"
.t insert end "a\tb\tc\tasdbcanasdasd\te\tf\tg\n"
.t tag configure wordprocessor -tabstyle wordprocessor
.t tag add wordprocessor 3.0 5.0
.t tag configure tabular -tabstyle tabular
.t tag add tabular 5.0 7.0

and here's an example showing how Tk 8.4 does not move you to the next tab stop to the right each time:

pack [text .t]
.t configure -tabs {0.25i}
.t insert end "[string repeat a 20][string repeat \tb 10]"

The above behaves completely differently in Tk 8.4 and 8.5 at present.

Implementation

An example implementation (minus tests and documentation) is available at SourceForge [1]. The bug report also contains some further discussion on this issue.

Copyright

This document has been placed in the public domain.

This is not necessarily the current version of this TIP.