Microsoft Excel Workbooks
A Microsoft Excel workbook that contains data in more than one worksheet, or that contains blank worksheets before the worksheet containing data, is stored as a frameset of two frames: a worksheet frame and a worksheet navigation tab frame. The frameset HTML file contains information about the workbook, links to supporting documents, and the frameset definition. In addition, the workbook HTML file contains default VBScript elements to support the tab functionality of the navigation tab frame. The worksheet frame contains the active worksheet HTML file. Each worksheet is stored in an HTML file. The tab frame is also stored in an HTML file and contains the tabs that allow the user to display each worksheet. A workbook is saved in a single HTML file if the first worksheet contains data and all other worksheets are blank. Additional supporting files, such as graphics files, or a cascading style sheet (CSS) for storing information about cell formatting, might be created when the workbook is saved as a Web page.
Excel worksheet data is represented in HTML tables. These tables can be modified directly to make changes to the worksheet in Excel. While changing these tables and adding scripts to the worksheet HTML files is possible, in general you should avoid modifying the workbook HTML files, supporting HTML files, or any script created by Excel. If you modify these elements, the HTML files will not work correctly, or in some cases the changes will be discarded by Excel before saving the workbook as HTML.