elementonly

Elementonly is a term encountered in SGML and XML contexts to describe an element content model that contains only child elements, with no character data (PCDATA) allowed inside the element. In practice, an element defined as element-only means its content must be a sequence of elements according to the declared model, and text nodes are not permitted at that level of the hierarchy.

In DTDs, element-only content is expressed by an element declaration that lists only element names in its content model. For example, a declaration such as <!ELEMENT book (title, author, chapter+)> specifies that a book contains a title, an author, and one or more chapter elements, in that order, with no text within the book element itself. This constrains the document structure and facilitates predictable parsing and validation.

Element-only content is contrasted with mixed content, where text can appear alongside elements (for example, #PCDATA can be interleaved with child elements). The distinction helps document designers enforce strict structural rules when text is not part of the element’s content model. While element-only content is common in well-structured data formats, many XML vocabularies use mixed content or allow text in various places, depending on the intended representation.

In XML Schema, the corresponding concept is achieved by defining a complex type with a sequence (or all) of element declarations and without mixed content, rather than by an explicit element-only keyword. The term remains most associated with traditional DTD-based validation and SGML-derived document design.