Block of content
A block of content in an HTML web page is a set of nodes from that page for which all the following are true:
- content: there is at least one node which is perceivable content in the block; and
- continuity: if two nodes are in the block, then any node between them (in tree order) is also in the block; and
- downward closure: if a node is in the block, then all its descendants are also in the block; and
- parent closure: if all children of a node are in the block, then this node is also in the block.
This definition assumes that the rendering order of nodes on a page does not greatly differ from the DOM tree order. Otherwise, blocks of content as defined here may be different from what is visually perceived as "content in a close relationship".