Feature request: Custom start for arabic cross reference numbering scheme

[maptv]

It would be great to add the ability to set the starting point for the arabic cross reference numbering scheme: https://quarto.org/docs/authoring/cross-reference-options.html#numbering

This is already possible for all of the other cross reference numbering schemes.

The two use cases for this would be to start a new document with zero-based numbering and to continue the numbers from an existing document in a subsequent document:

---
title: "New document with zero-based numbering"
crossref:
  labels: arabic 0
---

---
title: " Continuation to a document with X figures, Y tables, and Z code listings"
crossref:
  fig-labels: arabic X
  tbl-labels: arabic Y
  lst-labels: arabic Z
---

I can volunteer to work on a pull request if someone could direct me to the place where the cross reference numbering logic lives.

[cscheid]

@maptv Thanks for the offer, but you should be aware that this is a big project. The crossref system is pretty complicated, because it needs to work across a variety of formats. At the very least, we need to be able to support

• html
• latex
• typst
• docx

Each of these is a different system, and although you might only need one of those formats, we don't want to add features that only work on a single format. I'm saying this so that your expectations are calibrated. We also need you to be willing to sign a contributor agreement, as described here.

[maptv]

@cscheid, Thanks for the quick response. I sent the contributor agreement to JJ.

I think it makes sense to start with html and then work down the checklist:

• html
• latex
• typst
• docx

I see files like crossref.ts and list.ts. Where would I start working on this?

[cscheid]

(@maptv I moved this discussion to the relevant repo.)

You should start by installing the dev version of Quarto. The HTML crossref system is at least partly implemented in Lua in the Pandoc filters. Look at

quarto-cli/src/resources/filters/crossref/format.lua

Lines 137 to 222 in 861e3df

	function formatNumberOption(type, order, default)
	-- alias num and section (set section to nil if we aren't using chapters)
	local num = order.order
	local section = order.section
	if not crossrefOption("chapters", false) then
	section = nil
	elseif section ~= nil and section[1] == 0 then
	section = nil
	elseif crossref.maxHeading ~= 1 then
	section = nil
	end
	-- return a pandoc.Str w/ chapter prefix (if any)
	local function resolve(num)
	if section then
	local sectionIndex = section[1]
	if crossrefOption("chapters-alpha", false) then
	sectionIndex = string.char(64 + sectionIndex)
	elseif crossref.startAppendix ~= nil and sectionIndex >= crossref.startAppendix then
	sectionIndex = string.char(64 + sectionIndex - crossref.startAppendix + 1)
	else
	sectionIndex = tostring(sectionIndex)
	end
	num = sectionIndex .. "." .. num
	end
	return pandoc.Inlines({ pandoc.Str(num) })
	end
	-- Compute option name and default value
	local opt = type .. "-labels"
	if default == nil then
	default = stringToInlines("arabic")
	end
	-- See if there a global label option, if so, use that
	-- if the type specific label isn't specified
	local labelOpt = crossrefOption("labels", default);
	-- determine the style
	local styleRaw = crossrefOption(opt, labelOpt)
	local numberStyle = pandoc.utils.stringify(styleRaw)
	-- process the style
	if (numberStyle == "arabic") then
	return resolve(tostring(num))
	elseif (string.match(numberStyle, "^alpha ")) then
	-- permits the user to include the character that they'd like
	-- to start the numbering with (e.g. alpha a vs. alpha A)
	local s = split(numberStyle, " ")
	local startIndexChar = s[2]
	if (startIndexChar == nil or startIndexChar == " ") then
	startIndexChar = "a"
	end
	-- local startIndexChar = string.sub(numberStyle, -1)
	-- if (startIndexChar == " ") then
	-- startIndexChar = "a"
	-- end
	-- print(numberStyle)
	local startIndex = utf8.codepoint(startIndexChar)
	return resolve(utf8.char(startIndex + num - 1))
	elseif (string.match(numberStyle, "^roman")) then
	-- permits the user to express `roman` or `roman i` or `roman I` to
	-- use lower / uppper case roman numerals
	local lower = false
	if (string.sub(numberStyle, -#"i") == "i") then
	lower = true
	end
	return resolve(toRoman(num, lower))
	else
	-- otherwise treat the value as a list of values to use
	-- to display the numbers
	local entryCount = #styleRaw
	-- select an index based upon the num, wrapping it around
	local entryIndex = (num - 1) % entryCount + 1
	local option = styleRaw[entryIndex]:clone()
	if section then
	tprepend(option, { pandoc.Str(tostring(section[1]) .. ".") })
	end
	return pandoc.Inlines({ option })
	end
	end

That should get you a toehold.