paperspec/spec/03-nodes.md

3. Nodes

A document is a tree of nodes. nodes.jsonl holds one node per line, in document order: the root first, then each node before its children, and siblings in order.

3.1 The node record

Property	Required	Holds
id	Yes	The node ID (4).
kind	Yes	One of the kinds in 3.2.
parent	Yes	The parent's ID, or null for the root.
ord	Yes	The position among its siblings, from 0.
label	No	The printed label (2.3, Figure 2, (1), a), for kinds that take one.
attrs	No	Structural attributes, by kind (3.4).
content	No	The node's own content, by kind (3.3).
withheld	No	true when the policy withholds the content (12.5).
fidelity	No	For leaves, the level the pipeline established: F0, F1 or F2 (8.1).
prov	No	{witnesses, backend?, reading?, corroborated_by?}: the witness IDs the text came from, the backend, and the witnesses that agree.
text_hash, match_hash, align_key, own_hash, node_hash	Yes	The five content values (5).

Optional properties are omitted, never written as null. The schema is node.schema.json.

3.2 Kinds and children

Kind	May contain	Content	Label
document	front, section, back
front	title, authors, abstract, keywords, notes
title	sentence
authors		runs
abstract	blocks, section
keywords		runs
notes	footnote, paragraph
section	heading first, then blocks and section		Yes
heading	sentence
paragraph	sentence
sentence	equation	runs
equation	equation-line	math	Yes
equation-line		math	Yes
figure	panel, caption, figure-note		Yes
panel			Yes
caption	sentence
figure-note	sentence
table	caption, table-head, table-body, table-note		Yes
table-head, table-body	row
table-note	sentence
row	cell
cell		runs
list	item
item, quote	blocks
code, algorithm		verbatim	Yes
theorem	blocks		Yes
footnote	sentence		Yes
back	acknowledgments, references, appendix, notes
acknowledgments	blocks
references	reference
reference		runs	Yes
appendix	section

Blocks are paragraph, equation, figure, table, list, quote, code, algorithm, theorem and footnote.

These rules also hold:

1. Exactly one node is a root, and it is a document.
2. A heading is a section's first child, and a section has at most one.
3. front, back, title, authors, abstract, keywords, caption, table-head, table-body, acknowledgments and references occur at most once among their siblings.
4. A table has exactly one table-body.
5. title, heading, paragraph, caption, figure-note, table-note, table-head, table-body, row, list, item, quote, theorem, footnote and appendix have at least one child.
6. Only the kinds marked in the table take a label.
7. A body without headings, as in a letter, is a section with no heading.

Kinds outside this list are refused; a new kind is a minor version. Page breaks, running heads and columns are not nodes: they are geometry (7).

3.3 Content

Content	Kinds	Shape
Runs	sentence, cell, reference, authors, keywords	A non-empty list of inline runs (3.5).
Math	equation, equation-line	{notation, source}: tex or typst, and the source as written.
Verbatim	code, algorithm	{language?, text}.

Other kinds have no content. Derived renderings, such as MathML, are not content; they live in derived/ (12.7).

3.4 Attributes

Kind	Attribute	Holds
section	level (required)	1 for a section, 2 for a subsection, and so on.
table	columns	The column definitions: [{id, header_path}], where header_path lists header cell IDs, outermost first (9.2).
cell	column, rowspan, colspan, role	The column's ID, spans (default 1), and data (default), column-header, row-header or row-group-header.
row	header_path	The cell IDs that label the row, outermost first.
list	ordered	Whether the list is numbered.
item	marker	The printed marker.
theorem	variant	The printed kind: Theorem, Lemma, Definition, Proof, Remark.
panel	image, crop, figure_text	The image asset, a crop, and the text found inside the panel (9.1).

No other kind carries attrs, and each kind carries only its own attributes.

3.5 Inline runs

Run	Properties	Plain projection
text	text, and optional style: a sorted list of distinct values from em, strong, sup, sub, sc, mono, never both sup and sub.	The text.
math	notation (tex or typst), source.	$ + source + $
cite	refs: reference node IDs; text: the printed form, such as 23, [1,2] or (Smith, 2019).	The printed form.
xref	target: a node ID in this document, an address in another, or null when not yet resolved; text.	The printed form.
fnmark	footnote: a footnote's ID, or null; text: the mark.	The mark.
link	url, text.	The text.
equation	node: the ID of an equation child of the sentence.	$$ + that equation's source + $$

Runs are canonical: no text run is empty, and no two adjacent text runs have the same style list. A sentence's equation runs name its equation children, each once, in the children's order, and a sentence has no other children. A display equation the sentence runs through is thus part of the sentence, while keeping its own ID and hashes.

3.6 The plain projection

The plain projection of a node with runs is the concatenation of its runs' projections. That of an equation or an equation line is $$ + source + $$, and that of a verbatim node is its text. That of any other node is the plain projections of its text leaves joined with one U+0020.

A node's text leaves are found by walking its subtree in document order and stopping at sentence, cell, reference, authors, keywords, code and algorithm nodes, and at equation nodes whose parent is not a sentence; an equation-line is never a text leaf.

Offsets, quotations and the text hash are all defined on the plain projection as stored, before normalization.