We use the Gestalt principles of perception to decode the structure of a document visually. One task in making sense of a document is determining which elements are related and which are not. Uniform connectedness defines groups of related information, frequently using “common regions,” in which elements are grouped within a bounding box or uniform background.
Structural markup provides the means to use uniform connectedness to group elements in a nonvisual and machine-readable way. A list tag in essence draws a line around several items and asserts that they are related. The
<table> tag connects data in rows and cells into a single expression of a concept. Even the
<cite> tag surrounds a phrase and declares its relatedness as a book, magazine, or article title.
Using uniform connectedness both on the surface in the visual design and in the structural markup in underlying page code allows both visual and nonvisual users to make sense of the structure of a document.