A placeholder for content that is rendered in a specific part of the parent component, such as the
header or footer of an <apex:dataTable>.
An <apex:facet> component can only exist in the body of a parent component if the parent
supports facets. The name of the facet component must match one of the pre-defined facet names
on the parent component. This name determines where the content of the facet component is
rendered. Consequently, the order in which a facet component is defined within the body of a
parent component does not affect the appearence of the parent component.
See <apex:dataTable> for an example of facets.

Note: Although you can’t represent an <apex:facet> directly in Apex, you can specify it on a
dynamic component that has the facet. For example:

A.
apex:logCallPublisher

B.
apex:dataList

C.
apex:inputField

D.
apex:facet