Create RDFa structured data attributes for HTML elements as an alternative to JSON-LD and Microdata.
RDFa encodes structured data as plain HTML attributes: a `vocab` attribute points the page at a vocabulary such as Schema.org, and `typeof` and `property` attributes say what an element is and what its values mean. This generator takes a vocabulary, a type, and a set of properties, and returns ready-to-paste markup you can wrap around content you already have. The thing most people get wrong is placement: nested property attributes describe the nearest enclosing element that declares `typeof`, so moving a snippet onto a different element silently changes the meaning of the whole block.
A concrete input and expected output from the current implementation.
Input
Vocabulary: https://schema.org/ | Type: Person | name = Ada Lovelace, email = [email protected]
Expected output
<div vocab="https://schema.org/" typeof="Person"> <span property="name">Ada Lovelace</span> <span property="email">[email protected]</span> </div>
With `vocab` in scope, the bare tokens Person, name, and email expand against the vocabulary to https://schema.org/Person, https://schema.org/name, and https://schema.org/email. The div's `typeof` opens a new subject, and each `property` generates one triple whose object is the element's text content.
Each `property` attribute becomes a subject-predicate-object triple. The subject comes from the element's own `about` or `resource`, else from the nearest ancestor that introduced a subject with `typeof`. The predicate is the property token expanded against the vocabulary. The object is the element's text content, unless `content` overrides it, or `href` or `src` turns it into a URI.
`vocab` sets a default base for the whole subtree, so a bare token like `Person` resolves to `https://schema.org/Person`. `prefix` declares shorthand mappings such as `foaf: http://xmlns.com/foaf/0.1/` for vocabularies without a default. A token with no colon and no `vocab` in scope is treated as a relative URI reference, which is almost always a mistake.
RDFa keeps the data inside the markup it describes - no duplicate script block to keep in sync - which suits hand-maintained pages. But JSON-LD is the format Google currently recommends, and RDFa's behavior depends on subtle rules about subject inheritance, so for new projects JSON-LD is usually the lower-effort choice.
Both give the element's triples a URI subject. `about` is the conventional way to state that the markup describes a particular resource, often the page itself or an external thing, and it usually sits on the body or a wrapper element. `resource` is more often used with `typeof` to give a newly created subject a URI instead of a blank node. When both appear on one element, `about` takes precedence.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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