HTML and CSS Reference
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Much of the power of CSS is based on the parent-child relationship of elements. HTML
documents (actually, most structured documents of any kind) are based on a hierarchy
of elements, which is visible in the “tree” view of the document (see Figure 1-15 ). In
this hierarchy, each element fits somewhere into the overall structure of the document.
Every element in the document is either the parent or the child of another element, and
it's often both.
Figure 1-15. A document tree structure
An element is said to be the parent of another element if it appears directly above that
element in the document hierarchy. For example, in Figure 1-15 , the first p element is
parent to the em and strong elements, while strong is parent to an anchor ( a ) element,
which is itself parent to another em element. Conversely, an element is the child of
another element if it is directly beneath the other element. Thus, the anchor element
in Figure 1-15 is a child of the strong element, which is in turn child to the p element,
and so on.