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Re: Definitions for "viewport"

From: Greg Lowney <gcl-0039@access-research.org>
Date: Thu, 10 Oct 2013 09:51:04 -0800
Message-ID: <5256E908.5070301@access-research.org>
To: "Richards, Jan" <jrichards@ocadu.ca>
CC: WAI-UA list <w3c-wai-ua@w3.org>
Comments marked GCL:

-------- Original Message --------
Subject: Re: Definitions for "viewport"
From: Richards, Jan <jrichards@ocadu.ca>
To: WAI-UA list <w3c-wai-ua@w3.org>
Date: 10/10/2013 7:15 AM
> Hi Greg,
>
> Comments marked JR:
>
> From: Greg Lowney [mailto:gcl-0039@access-research.org]
> Sent: October-10-13 4:15 AM
> To: WAI-UA list
> Subject: Definitions for "viewport"
>
> I think there are problems with the definitions of viewport and top-level viewport. They're complicated and pretty confusing in many respects.
>
> These currently read
> viewport: The part of an onscreen view that the user agent is presenting onscreen to the user, such that the user can attend to any part of it without further action (e.g. scrolling). There may be multiple viewports on to the same view (e.g. when a split-screen is used to present the top and bottom of a document simultaneously) and viewports may be nested (e.g. a scrolling frame located within a larger document). A container can hold multiple viewports at the same nesting level. When the viewport is smaller in extent than the content it is presenting, user agents typically provide mechanisms to bring the occluded content into the viewport (e.g. scrollbars).
>
> top-level viewport: A viewport that is not contained within another user agent viewport.
>
> 1. I think they should do more to clarify whether or not a browser's window is a viewport, or whether only the areas within it that render content are viewports. That also affects whether, in a browser that uses tabbed panes to display multiple documents or views of the same document, whether these tabbed panes are top-level viewports. 1.8.13 says "top-level viewports (e.g. windows or tabs)", but since browser windows typically contain user agent user interface as well as rendered content, this only works if viewports also include browser windows; if they don't, then this occurrence would be wrong and need to change.
>
> JR: Agree we should clarify.
>
> 2. I find the phrase "The part of an onscreen view that the user agent is presenting onscreen to the user" confusing, particularly in light of the definition of "view". That is, is it a portion of the rendered content or presented content source, or is it the pane or bounded region used to display those? It is the pane (or container) that the user resizes, not the content. The "part of an onscreen view that the user agent is presenting onscreen to the user" may only takes up a little space in this pane, but it's the pane which has controls to let the user resize it (e.g. drag handles), not the content inside the pane.
>
> JR: I agree it's a confusing way to start the definition, but I'm having
>
> 3. It uses the term "container" which is not defined, and I don't think used in a universally-understood sense. The document sometimes uses "container" to mean a component of the user agent user interface, such as a toolbar, and here it seems to mean a component of the user agent user interface such as a browser window, but in 2.1.1 it's used as a synonym for viewport.
>
> JR: I don't think "container" is needed for the defn.
GCL: I might not have made it clear that we should also consider normalizing our text so that the use of container in 2.1.1 doesn't conflict with usage elsewhere.
>
> 4. This definition of viewport is limited only to "onscreen" presentations, but elsewhere don't we talk about non-visual viewports? If we didn't, why would we so often say "graphical viewports"? Views are defined as being "A view can be visual, audio, or tactile", and what would the non-visual ones be presented in if not a viewport?
>
> JR: By its nature, I don't think audio can have a viewport. I searched "audio viewport" and found this patent (https://www.google.com/patents/US20100245257)... But I think its just audio labels on key points of a visual viewport. There can be a tactile viewport.
>
> 5. If one viewport has scrolling, then strictly according to the definition any viewport nested inside it would cease to be a viewport once it's scrolled out of view, because the definition says "such that the user can attend to any part of it without further action (e.g. scrolling)". Well, it's scrolled out of view, so you have to use scrolling before you can attend any part of it. (If it's scrolled so it's only partially visible, then only the visible portion would seem to be viewport.
>
> JR: If a tree falls in the forest... :)
>
> OK, here's another kick at the can...
>
> viewport:
> A mechanism for presenting only part of a visual or tactile view to the user via a screen or tactile display. There may be multiple viewports on to the same underlying view (e.g. when a split-screen is used to present the top and bottom of a document simultaneously) and viewports may be nested (e.g. a scrolling frame located within a larger document). When the viewport is smaller than the view it is presenting, some of the view will not be presented. Mechanisms are typically provided to move the view or the viewport such that all of the view can be brought into the viewport  (e.g. scrollbars).
> Note: In UAAG 1.0 viewports were defined as having a temporal dimension. In UAAG 2.0, this is not the case. Since audio content is inherently time-based, audio viewports are excluded.

GCL: That sounds good.
>
> top-level viewport:
> A viewport that is not contained within another viewport of a *platform-based user agent*. A popular browser implementation is to provide a window that includes some user agent user interface elements (e.g., menus) and a series of tabbed panels, each of which contains additional user agent user interface elements (e.g., address bar, bookmarks, back/forward buttons) and a top-level viewport for rendering a view of the addressed web resource.

GCL: We might clarify by adding after the first sentence something like "(Web-based user agents are always displayed inside another viewport, and therefore are not top-level.)"; that way the user doesn't have to spend a few seconds pondering why it is limited to platform-based user agents. Otherwise it's great. (Interestingly, I've never thought of the toolbars and status bar as being inside the tabbed panels with the viewport, so that part of the definition gave me pause, but either perspective works.)

>
> View: (UNCHANGED)
> A user interface function that lets users interact with web content. UAAG 2.0 recognizes a variety of approaches to presenting the content in a view, including:
> - rendered view: A view where content is presented such that it is rendered, played or executed. There are two sub-types:
>    + In conventionally rendered views the content is rendered, played or executed according to the web content technology specification. This is the default view of most user agents.
>    + In unconventionally rendered views the content is rendered quite differently than specified in the technology specification (e.g. rendering an audio file as a graphical wavefront).
> - source view: A view where the web content is presented without being rendered, played or executed. The source view may be plain text (i.e. "View Source") or it may include some other organization (e.g. presenting the markup in a tree).
> - outline view: A view where only a subset of the rendered content is presented, usually composed of labels or placeholders for important structural elements. The important structural elements will depend on the web content technology, but may include headings, table captions, and content sections.
> Note: A view can be visual, audio, or tactile.
>
> Cheers,
> Jan
>
Received on Thursday, 10 October 2013 16:51:11 UTC

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