Accessibility should be a part of the Web design process instead of being a post-design repair process. Thus, it should be more integrated within the internal authoring tools� mechanism of generating new Web contents. Web composition, when creating Web pages from data extracted from heterogeneous or external sources, should have accessibility into account in order to guarantee that the final page being constructed is accessible. This paper presents the rules that, in a composition process, a design tool must guarantee in order to create accessible Web pages. We also present WSLS as an accessibility enabled authoring tool that makes this task feasible, and focus in how this tool incorporates accessibility into the process of generating new Web contents.