TIP #256: IMPLEMENT TABULAR AND WORDPROCESSOR STYLE TABBING 
=============================================================
 Version:      $Revision: 1.15 $
 Author:       Vince Darley <vince_at_santafe.edu>
               Vince Darley <vincentdarley_at_users.sourceforge.net>
 State:        Final
 Type:         Project
 Tcl-Version:  8.5
 Vote:         Done
 Created:      Friday, 12 August 2005
 URL:          https://tip.tcl-lang.org256.html
 Post-History: 

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 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 (except for the special /-tabs {}/ 
 case, which uses wordprocessor style 8-tabs!), although none of this is 
 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. 

 As a result of this change, abbreviations such as *-ta* or *-tab* will 
 become ambiguous and trigger an error. This is considered a bug in the 
 calling script (and a trivial thing to fix in such scripts). Similar 
 ambiguities have been introduced by TIPs in the past (e.g. with 
 /grid/). It may actually be a useful ambiguity, in that it will alert 
 script writers to the fact that new tabbing functionality is available, 
 and in particular that a decision on desired tab style needs to be 
 made. 

 In addition the strange difference in Tk 8.4 between an empty *-tabs* 
 value and any other value will be changed for Tk 8.5 - it will use the 
 *-tabstyle* option to determine how to interpret tabs under all 
 circumstances, and use the *-tabs* list simply to determine the 
 location of the tab stops. 

 Here's an example usage: 

   pack [text .t]
   .t configure -tabs {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 
================

 A full implementation, with documentation and tests is available at 
 SourceForge 
 [<URL:http://sf.net/tracker/?func=detail&aid=1247835&group_id=12997&atid=112997>]. 
 The bug report also contains some further discussion on this issue. 

 COPYRIGHT 
===========

 This document has been placed in the public domain. 

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