2. The computer system of claim 1, wherein the requested document is an 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.
2. The computer system of claim 1, wherein the requested document is an 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. 5. The computer system of claim 2, wherein: the requested document is defined in a first markup language, the output document is defined in a second markup language; the system further comprises means for accessing a mapping table which defines how to map elements in the first markup language to elements in the second markup language; and the means for combining includes means for converting the selected portion of the requested document from the first markup language to the second markup language using the mapping table.