TPS was a structured document editor. That is, it internally treated a document as a set of element classes, each with its own set of properties. Classes might include common document elements such as a body, paragraphs, titles, subheadings, captions, etc. Authors were free to create any set of elements and save them as a reusable template. The properties of a class — its font size, for example — could be changed and automatically applied to every instance of that class. If this caused a change in pagination — increasing the font size could change where the page breaks were — the software would update the screen quickly enough for the author to continue typing, including altering all of the cross-references that the author may have inserted; this WYSIWYG capability was a competitive advantage for the company. The structured nature of the documents also enabled TPS to provide "conditional document assembly", a feature that enabled users to "tag" document elements with metadata about them, and then automatically assemble versions of the document based upon those tags. For example, an aircraft manufacturer might tag paragraphs with the model number of the planes to which they applied and then assemble versions of the documentation specific to each model.