render_element
static void render_element(FILE *out, struct element *e, struct element *tag);
render_element(NULL, root->element, NULL);
render_element(out, root->element, NULL);
render_element(out, ce, NULL);
render_element(out, e->children, e);
render_element(out, e->type->type->element, tag);
render_element(out, ec, NULL);
render_element(out, e->children, NULL);
render_element(out, ec, ec);