Greetings!Here is some possible errata:In the section, "Using substitutionGroup" at URL http://www.w3schools.com/schema/schema_complex_subst.asp , it seems that example code should be there. The subsequent section, "What are Global Elements?" also seems to be lacking some context.I'd also like to make two recommendations:1) Allow the layout to expand (e.g., via percentage widths). For larger monitors, many of us would like to be able to view more on the page at once, and the current fixed-width layout constrains that.2) Add a Mozilla XUL tutorial (and the related scripting, etc. of it) and Ser