23. The system of claim 20, wherein: the requested document is defined in a first markup language, and the output document is defined in a second markup language; the system further includes a table accessing component which provides access to a mapping table which defines how to map elements in the first markup language to elements in the second markup language; and the data processing component includes a data converting component which receives the selected portion of the requested document in a first markup language at an input and produces the selected portion in a second markup language at an output, the data converting component using the mapping table.
20. The computer system of claim 19, wherein the requested document is a digital document having fixed text content and fixed structure defined by descriptive markup defining a plurality of hierarchical elements providing an indication of structure of the digital document.