1. A computer-implemented method for providing thematic information to provide a visual theme for documents, comprising: defining a theme object for conveying theme elements to documents; wherein the theme object is defined using a markup language and stored in a theme file; wherein the definition of the theme object in the theme file is maintained separately from other objects that define the document; wherein the other objects comprise: a features part; a data part; and a styles part; wherein the theme object definition includes properties that can be shared and overridden in a hierarchical manner; wherein a schema defines and enforces rules for displaying the theme object; using a first application to author a first document and associating the theme object in the theme file with the first document; wherein the first document is associated with a first file format that includes modular parts that are associated together via a first document relationship hierarchy; wherein the theme object is a modular part that is associated with the first file format via the first document relationship hierarchy; and using a second application that is different from the first application to author a second document and associating the theme object in the theme document with the second document wherein the second document is associated with a second file format that includes modular parts that are associated together via a second document relationship hierarchy; wherein the theme object is a modular part that is associated with the second file format via the second document relationship hierarchy, such that a single theme object is associated with multiple file formats and documents; wherein associating the theme object in the theme document with the first document and the second document applies the theme elements to the first document and the second document such that the first document and the second document have a common appearance.
3. The method of claim 1 wherein the theme elements comprise information for colors, fonts, and formatting of a document.