If you have worked with VSeWSS templates you will have probably noticed the comment added to the top of certain aspx/xml files:

First of all don't delete this! This "comment" is actually meta data that enables the VSeWSS solution builder to process the file. The "_filecategory" property identifies the file category (I have a gift for stating the obvious...). It is actually tied the the SolutionElementFileCategory in the SPDevTools.dll library under the Microsoft.SharePoint.Tools.SharePointSolutions namespace.

public enum SolutionElementFileCategory

Next, the "_filetype" identifies the type of file (Duh!) and is tied to the SolutionElementFileType enumeration in the library/namespace mentioned previously.

public enum SolutionElementFileType

Next, the "_filename" property tells the solution builder what the name of the file should be in the resulting solution. And last but not least the guid which uniquely identifies the file. Every element in a solution must have a unique guid in order for the solution builder to work with it ("Element" meaning a SP Solution aspx/xml file or a class). Classes are given a unique identifier by defining a Guid attribute to the class. If you copy an existing aspx/xml solution file, as a template for a new file, remember to change the guid. Also if you are copying a solution file as a template for a new module file don't forget to remove the meta data. If you don't, the solution builder will not include it in the module as it thinks the file has another purpose because of the metadata.