The semantic hierarchy of a document written in a markup language is represented by a hierarchy of elements, which are viewed and edited using a tree view editor. Each element is represented as a node of a semantic tree, to which may be attached a special purpose editor, capable of editing the semantic properties of that particular element. Such special purpose editors handle the single element to which they are attached and may handle a hierarchy of elements that share common properties in the subtree headed by the single element. They offer a visualization of the elements to which they are attached that is not necessarily hierarchical in form.