Many features of the Word Binary File Format pertain to a range of CPs (section 2.2.1). For example, a bookmark is a range of CPs (section 2.2.1) that is named by the document author. As another example, a field is made up of three control characters with ranges of arbitrary document content between them.
The Word Binary File Format uses a PLC structure (section 2.2.2) to specify these and other kinds of ranges of CPs (section 2.2.1). A PLC (section 2.2.2) is simply a mapping from CPs (section 2.2.1) to other, arbitrary data.