function mk_block_toSource() {
  return "Markdown.mk_block( " +
          uneval(this.toString()) +
          ", " +
          uneval(this.trailing) +
          ", " +
          uneval(this.lineNumber) +
          " )";
}
toHTMLTree( markdown, [dialect] ) -> JsonML
 toHTMLTree( md_tree ) -> JsonML
 - markdown (String): markdown string to parse
 - dialect (String | Dialect): the dialect to use, defaults to gruber
 - md_tree (Markdown.JsonML): parsed markdown tree

 Turn markdown into HTML, represented as a JsonML tree. If a string is given
 to this function, it is first parsed into a markdown tree by calling
 [[parse]].