document_view, view_state... what's the difference?

In ELinks, we have various interrelated structures:
- struct document
- struct view_state
- struct document_view
- struct ecmascript_interpreter
- struct location

struct document is a canvas on which a (usually HTML) document
has been rendered for some charset.  It can be displayed on a
terminal with minimal conversions.  It can be kept in the
formatted document cache when it is not being displayed.
It can be displayed in multiple tabs at the same time, I think.
But then there is also document.timeout, which AFAIK should be
local to each tab.

struct location is what is kept in the history of each tab.

I don't understand why we have both struct view_state and struct
document_view.  When we're adding a member, how do we decide in
which of the two structures it belongs?

Back in August 2008, I searched for code that connects these
structures to each other or disconnects them again, and wrote the
following notes.  But I'm sad to say that I didn't get anywhere
From there.

IIRC, this is relevant to bug 765 or 771.


struct document *document_view::document;
	DETACH detach_formatted: doc_view->document = NULL;
struct view_state *document_view::vs;
	ATTACH render_document: doc_view->vs = vs;
	DETACH render_document: vs->doc_view->vs = NULL;
	ATTACH render_document: doc_view->document = document;
	DETACH ses_forward: vs->doc_view->vs = NULL;
	ATTACH draw_formatted: ses->doc_view->vs = &cur_loc(ses)->vs;
	ATTACH goto_mark: vs->doc_view->vs = vs;
	DETACH detach_formatted: doc_view->vs = NULL;
	DETACH destroy_vs: vs->doc_view->vs = NULL;
struct document_view *view_state::doc_view;
	DETACH render_document: vs->doc_view = NULL;
	ATTACH render_document: vs->doc_view = doc_view;
	DETACH ses_forward: vs->doc_view = NULL;
	ATTACH goto_mark: vs->doc_view = doc_view;
	DETACH detach_formatted: doc_view->vs->doc_view = NULL;
	DETACH destroy_vs: vs->doc_view = NULL;
	ATTACH copy_vs: copy_struct(dst, src);
	DETACH copy_vs: dst->doc_view = NULL;
struct ecmascript_interpreter *view_state::ecmascript;
	DETACH ecmascript_put_interpreter: interpreter->vs->ecmascript = NULL;
	ATTACH ecmascript_reset_state: vs->ecmascript = ecmascript_get_interpreter(vs);
	RETACH goto_mark: vs->ecmascript = ecmascript;
	DETACH copy_vs: dst->ecmascript = NULL;
struct view_state location::vs;
	FOLLOW render_document_frames: vs = &cur_loc(ses)->vs;
	FOLLOW render_document_frames: cur_loc(ses)->vs.current_link = n;
	FOLLOW l_current_url: struct view_state *vs = &cur_loc(lua_ses)->vs;
	FOLLOW script_hook_pre_format_html: struct view_state *vs = &cur_loc(ses)->vs;
	FOLLOW smjs_elinks_get_view_state: vs = &cur_loc(smjs_ses)->vs;
	MODIFY copy_location: copy_vs(&dst->vs, &src->vs);
	MODIFY destroy_location: destroy_vs(&loc->vs, 1);
	FOLLOW reload: loc->vs.ecmascript_fragile = 1;
	FOLLOW ses_forward: vs = &loc->vs;
	FOLLOW draw_frames: l = &cur_loc(ses)->vs.current_link;
	FOLLOW next_frame: vs = &cur_loc(ses)->vs;
LIST_OF(struct frame) location::frames;
struct view_state frame::vs;
	FOLLOW format_frame: vs = &frame->vs;
	MODIFY try_resolve_frame: ecmascript_reset_state(&target->vs);
	MODIFY copy_location: copy_vs(&new_frame->vs, &frame->vs);
	MODIFY destroy_location: destroy_vs(&frame->vs, 1);
	MODIFY request_frame: init_vs(&frame->vs, uri, -1);
	FOLLOW reload: vs = &frame->vs;


CALLER GRAPHS
-------------

detach_formatted
	// Parameter struct document_view *doc_view; detaches that from view_state and document.
	render_document
		// Parameters struct view_state *vs and struct document_view *doc_view;
		// attaches those to each other, calling detach_formatted(doc_view) and
		// detaching vs from any other document_view.
		format_frame
			format_frames
				@format_frames
				@render_document_frames
		@render_document_frames
		@dump_formatted
	render_document_frames
		update_status
			change_hook_insert_mode
				change_hooks...
			change_hook_ui
				@change_hooks
			unibar_set_property
				menubar_class...
				statusbar_class...
			init_session
				init_saved_session
					decode_session_info <INTERLINK_NORMAL_MAGIC>...
				decode_session_info
					handle_interlink_event <EVENT_INIT>...
				do_follow_url
					follow_url
						goto_uri...
						goto_uri_frame...
						goto_imgmap...
			tabwin_func <EVENT_ABORT>...
		l_current_document_formatted
			init_lua
		draw_formatted
			change_hook_css...
			toggle_document_option...
			show_http_error_document...
			display_timer...
			doc_loading_callback...
			tabwin_func <EVENT_REDRAW>...
			do_action <ACT_MAIN_BACKSPACE_PREFIX>...
			do_action <ACT_MAIN_FRAME_NEXT>...
			do_action <ACT_MAIN_FRAME_PREV>...
			do_action <ACT_MAIN_RERENDER>...
			text_typeahead_handler...
			link_typeahead_handler...
			toggle_plain_html...
			toggle_wrap_text...
			try_prefix_key...
			do_mouse_event...
	destroy_session
		tabwin_func <EVENT_ABORT>...
	dump_formatted
		dump_loading_callback
			dump_start
				dump_next
					@dump_loading_callback
					@dump_start
					init...
copy_vs
	copy_location
		@ses_forward
	setup_session
		@init_session
	@goto_mark
	@set_mark
ecmascript_put_interpreter
	ecmascript_reset_state...
		@render_document
		ecmascript_protocol_handler...
		js_try_resolve_frame...
		window_get...
		try_resolve_frame...
		window_get_property...
		call_onsubmit_and_submit...
	destroy_vs
		destroy_location...
			free_history...
			clean_unhistory...
			ses_history_move...
			@ses_forward
		setup_session...
		ses_forward
			tp_display...
			setup_download_handler...
			do_move <TASK_RELOAD>...
		@dump_formatted
		goto_mark
			try_mark_key <KP_MARK_GOTO>
				frame_ev_kbd
					frame_ev <EVENT_KBD>
						send_to_frame...
							do_mouse_event...
							send_kbd_event
								send_event...
		free_mark_by_index...
			set_mark
				@try_mark_key <KP_MARK_SET>
			done_marks...

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