Generally, these control characters were extremely application-specific, and it was difficult to treat sources marked up in one of these systems with one of the others. On the other hand, this type of markup does a very good job of defining the specific physical representation of a document, and for certain kinds of documents it might be more convenient for obtaining a given layout, in allowing a precise control of line and page breaks. This approach makes viewing and printing documents particularly easy, but re-using the source for other purposes can be difficult, even impossible. To successfully prepare a document for use in multiple ways it is mandatory to clearly describe its logical structure by eliminating every reference to a physical representation. This is what is understood under the term logical or generic markup.
Figure shows a few examples of marking up the same text.