The inventive editor allows web authors to edit HTML visually while preserving the HTML source document. The editor preserves the structure and format of the HTML, and permits simultaneous modeless visual and source document editing. When an edit is made with the invention, only the HTML source around that edit is updated, rather than rewriting the whole HTML source document. Furthermore, when an edit is made, the new HTML source code is outputted in a format that is specified by the user. In order to preserve the format of the document, format information is stored in the parsed tree. The format of the node is preserved when its source is regenerated; edits to the node will reformat it according to user preferences. In order to preserve the structure of the document, invalid HTML structures are maintained and not corrected. The invention will either support the invalid structure by reflecting such structure in the parsed tree, and thus allow for editing of the structure, or the invention will not support such a structure, and represent such structures as invalid nodes. Moreover, the invention also maintains structure while editing, as the structure and format of the document is only minimally modified during editing, i.e. only the nodes affected by the edits are restructured and reformatted, and the remainder of the document is unmodified.