Citation as a strict subset of CSL-JSON v1.0.2
The style-graphql skill's canonical Citation GraphQL type is documented, in its own bundled reference file, as a "strict subset of CSL-JSON v1.0.2" (citation-style-language/schema). It maps 1:1 to a Citation Zod schema (src/style-skills/citation.schema.ts) elsewhere in that skill's own codebase -- the GraphQL SDL, in other words, is one of at least two typed projections of the same underlying citation shape, the same "projection" concept the skill's own contract functions (parse/stringify/roundtrip) are named for.
What "strict subset" means here
CSL-JSON v1.0.2 defines 46 citation item types in its full specification. The CSLType enum in this skill's SDL carries only 17 of them -- ARTICLE_JOURNAL, ARTICLE_MAGAZINE, ARTICLE_NEWSPAPER, BOOK, CHAPTER, DATASET, DOCUMENT, MANUSCRIPT, PAPER_CONFERENCE, POST_WEBLOG, REPORT, SOFTWARE, SPEECH, STANDARD, THESIS, TREATY, WEBPAGE -- explicitly documented in the reference file as "a subset covering the most common citation types." Similarly, Citation.author uses a simplified CSLName shape (family/given/literal) rather than the full CSL-JSON name-particle grammar, and Citation.issued's CSLDate mirrors CSL-JSON's own date-parts nested-array convention ([[year, month?, day?], ...]) plus a literal fallback.
The Anthropic and W3C bridge fields
Two fields extend past plain CSL-JSON: Citation.anthropic (an AnthropicCitationBridge type) carries the real Anthropic Citations API response shape -- documentIndex, documentTitle, character span (startCharIndex/endCharIndex), and the verbatim citedText Claude cited -- and Citation.prov (a ProvO type) carries a W3C PROV-O fragment (wasDerivedFrom, generatedAtTime, wasAttributedTo). Both are documented directly in references/citation.graphqls's own doc comments, not inferred.
Full type definitions: browse the type catalog. Source: style-graphql skill, SKILL.md + references/citation.graphqls.