subelements

Subelements are components contained within a parent element in hierarchical data structures. The term is widely used in markup languages such as XML and HTML, where elements can be nested inside other elements. Subelements are also referred to as child elements or nested elements, depending on the context. Beyond markup, many data formats such as JSON and YAML express hierarchy through nested objects and arrays, which serve a similar purpose.

In a tree-like structure, a parent element may have zero or more subelements, and each subelement may itself have subelements, forming a nested hierarchy. Subelements carry data and may support attributes (in XML) or text content. The order of subelements can be significant in schemas that enforce sequences, while other schemas treat subelements as unordered values.

In XML and HTML, subelements are defined by nesting tags: for example, a book element may contain title and author subelements. Subelements define document structure and semantics, and in HTML they contribute to the DOM and rendering.

Processing and querying subelements involves various tools and standards. Document Object Model (DOM) and streaming parsers (SAX, StAX) read subelements, while path-like languages such as XPath or JSONPath select them. Schemas such as XML Schema Definition (XSD) and DTD describe allowed subelements and their occurrence constraints, including minOccurs and maxOccurs.

In other contexts, the term is used in user interface design to describe component trees, where a container element hosts subelements such as headers, bodies, or controls. The concept is central to data modeling and document formats; in chemistry, "subelements" is not a standard term for substructures.