Padded numbering in Writer, part 2

Posted on: Wed 08 April 2020

Estimated read time: 2 minutes

I already posted about the start of padded numbering support in Writer, there the focus was to insert 0 characters to pad up the result to 2 characters. Let’s see how that got extended in the recent past…

First, thanks Nicolas Christener who made this work by Collabora possible.

Motivation

Padded numbering is a style where you insert 0 characters in front of an otherwise normal (Arabic) numbering, making sure that the result always has at least N characters. Up to now, you had to number your content manually to have this effect, while Word supports this feature.

OOXML supports padding up to 2, 3, 4 and 5 characters. The news is now now it’s possible to not only pad up to 2 characters, but also to any number between 2 and 5.

Results so far

Here is how the current rendering of padded numbering looks like, with a custom prefix and suffix:

https://lh3.googleusercontent.com/JHqkVdHkLLkFV1Mrh5jR1FFqq8PvU3lmjuOrl6SwBnM-ygsbugL-FccMHIod9Uyj2-hAyADRX7VwozUHgzBTZTdo72FB_nuHzEH-iQngSl5ND0o6h1sZDTs1uv8H5cLNv0cHDgRv2A=w640

Figure 1. numbering-padded4.docx, current rendering

You can see how 0 is inserted before 999, but not before 1000 as this is the pad-to-4 case.

How is this implemented?

If you would like to know a bit more about how this works, continue reading… :-)

Padding to a custom number is not something that works in general, because both ODF and OOXML has a separate number format for each padding. So Writer supports the 4 cases Word supports, but (for now) not more.
Padding to 3 or more is more complicated than pad to 2, because OOXML has different markups for them.

Here is how the pad-to-2 markup looks like:

      <w:numFmt w:val="decimalZero"/>

And here is how you define pad-to-3:

      <mc:AlternateContent>
        <mc:Choice Requires="w14">
          <w:numFmt w:val="custom" w:format="001, 002, 003, ..."/>
        </mc:Choice>
        <mc:Fallback>
          <w:numFmt w:val="decimal"/>
        </mc:Fallback>
      </mc:AlternateContent>

This required taking the w14 branch when we hit such a conditional, we used to read the fallback branch previously.
This required mapping the data of the <w:numFmt> XML element not to an enumeration value, but to a pair of objects: the numbering format’s value and format.

The rest was reasonably straightforward, since the actual padding implementation just had to be generalized.

Want to start using this?

You can get a snapshot / demo of Collabora Office and try it out yourself right now: try unstable snapshot. Collabora is a major contributor to LibreOffice and all of this work will be available in TDF’s next release too (7.0).

Category: libreoffice – Tags: en