functionality without jeopardizing backward and forward compatibility. Despite the fact that the newer version is extremely rich in functionality, WordPerfect X5 documents are fully compatible with WordPerfect 6.0a documents in both directions. The older program simply ignores the "unknown" codes, while rendering the known features of the document. WordPerfect users were never forced to upgrade for compatibility reasons for more than two decades. Streaming code architecture A key to WordPerfect's design is its streaming code architecture that parallels the formatting features of HTML and Cascading Style Sheets. Documents are created much the same way that raw HTML pages are written, with text interspersed by tags (called "codes") that trigger treatment of data until a corresponding closing tag is encountered, at which point the settings active to the point of the opening tag resume control. As with HTML, tags can be nested. Some data structures are treated as objects within the stream as with HTML's treatment of graphic images, e.g., footnotes and styles, but the bulk of a WordPerfect document's data and formatting codes appear as a single continuous stream. A difference between HTML tags and WordPerfect codes is that HTML codes can all be expressed as a string of plain text characters delimited by greater-than and less-than characters, e.g. <strong>text</strong>, whereas WordPerfect formatting codes consist of hexadecimal values. Styles and style libraries The addition of styles and style libraries in WP 5.0 provided greatly increased power and flexibility in formatting documents, while maintaining the streaming-code architecture of earlier versions. Styles are a preset arrangement of settings having to do with things like fonts, spacings, tab stops, margins and other items having to do with text layout. Styles can be created by the user to shortcut the setup time when starting a new document, and they can be saved in the program's style library. Prior to that, WordPerfect's only use of styles was the Opening Style, which contained the default settings for a document. After the purchase of the desktop publishing program Ventura, Corel enhanced the WordPerfect styles editor and styles behavior with the majority of Ventura's capabilities. This improved the usability and performance of graphic elements like text boxes, document styles, footer and header styles. Since WordPerfect has been enriched with properties from the CorelDraw Graphics suite, graphic styles are editable. The Graphics Styles editor enables customizing the appearance of boxes, borders, lines and fills and store the customized design