Space before citations in Openoffice/Libreoffice integration

[lwlR]

By default, zero width space is added in front of each citation in the text in Openoffice/Libreoffice. This causes ugly line breaks if new line starts with a citation:

To allow changing if a zero width space is added to each citation, a new boolean in the style file can be used:
SpaceBefore="true" -> Default behaviour with the zero width space
SpaceBefore="false" -> No space is added:

Pull request to documentation added.

Mandatory checks

• Change in CHANGELOG.md described in a way that is understandable for the average user (if applicable)
• Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• Screenshots added in PR description (for UI changes)
• Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.

[Siedlerchr]

Thanks for your contribution, lgtm so far. Can you please update the documentation as well?
https://docs.jabref.org/cite/openofficeintegration#the-style-file

You can edit it by clicking on the 3 dots:

[calixtus]

Great feature. Thank you for digging into this!

[antalk2]

Two comments

• ZERO_WIDTH_SPACE = "\u2060" // "WORD JOINER"
  would probably solve the above problem without a need for an extra flag (SpaceBefore)

• Unfortunately I cannot exactly remember why I introduced the ZERO_WIDTH_SPACE. Whatever that was,
  SpaceBefore="false" might reintroduce it. On the other hand: if it causes no problems, than ZERO_WIDTH_SPACE
  is not needed (unless the user wishes to directly format the citation mark to something it otherwise would not inherit).

Details below

The problem solved by SpaceBefore="false"

At first, I did not understand the problem solved here.
Now I think I do:

LibreOffice

• can break the line after a zero width space (ZERO_WIDTH_SPACE = "\u200b") and
• when justifying a line considers this otherwise invisible ZERO_WIDTH_SPACE a word, thus leaves some space before it.
  This makes the visible line endings ragged.

"WORD JOINER"

Question: would it help if we used the "WORD JOINER" U+2060 ("\u2060") (https://unicode-explorer.com/c/2060) instead?

• At an automatic line break (after a space), the "WORD JOINER" character sticks to the next (non-space) character, i.e. it is not positioned before the automatic line break, thus does not create ragged lines.
• If there is no space before the "WORD JOINER", then there is no automatic line break created before it.

(Tested in LibreOffice 7.6.4.1 by inserting a "WORD JOINER" by copying it from https://unicode-explorer.com/c/2060)

So yes, changing the value of ZERO_WIDTH_SPACE to "\u2060" would probably solve the problem without
using the SpaceBefore flag introduced here (assuming citation markers never start with a space).

Does ZERO_WIDTH_SPACE matter? (Why did I introduce the ZERO_WIDTH_SPACE?)

• When we update a citation mark, its text is removed and the new text is inserted.
• The new text inherits its character formatting from "the context".
• If there is a character (within the same paragraph) before the insertion point, it provides "the context" for this inheritance. If there is none, LO looks somewhere else (maybe the character after the insertion point, and if the is none, then ...)

So what the ZERO_WIDTH_SPACE achieves is that if the user directly formats the citation mark -- in particular the invisible space at the beginning -- to for example highlighted, then the above procedure will preserve this (and extend it to the whole marker when updated) .

Well, this sounds nice, but only moderately important: SpaceBefore=false should be basically OK unless the user wishes to directly format the citation mark.

Yet, I have a vague recollection of introducing this ZERO_WIDTH_SPACE after making cleanFillCursor to remove the brackets (REFERENCE_MARK_LEFT_BRACKET and REFERENCE_MARK_RIGHT_BRACKET), because of some actual problem I encountered (as opposed to theoretical worries).