Sewing patterns are a form of technical document, requiring expertise to author and understand. Digital patterns are typically produced and sold as PDFs with human-interpretable vector graphics, but there is little consistency or machine-readable metadata in these documents. A custom file format would enable digital pattern manipulation tools to enhance or replace a paper based workflow. In this vision paper, basic sewing pattern components and modification processes are introduced, and the limitations of current PDF patterns are highlighted. Next, an XML-based sewing pattern document format is proposed to take advantage of the inherent relationships between different pattern components. Finally, document security and authenticity considerations are discussed.