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suggested clarification of viewport (affects point of regard)

From: Al Gilman <asgilman@access.digex.net>
Date: Wed, 11 Nov 1998 22:08:36 -0500 (EST)
Message-Id: <199811120308.WAA03764@access2.digex.net>
To: w3c-wai-ua@w3.org
What I have written about in the past as a "viewport" is missing
from the definitions below.  This is quite simply the set of
characters currently displayed through a Braille device or the
set of pixels currently displayed through a screen magnifier.

Mark's note is good.  What he described I might call a "reading
cursor."  It is a checkpoint -- where you would restart if
interrupted.

The chunks that the browser divides the document up into to speak
in step mode are de_facto document elements that are not
necessarily given by the markup but may be affected by browser
heuristics as well.  The viewport defined this way is an added
feature of the screen window that the browser paints.  It needs
to be recognized as a complication of the screen virtual device
and dealt with intelligently.

The guideline that says the user agent should not move the
selection or focus outside the viewport applies to the viewport
as described here.  Probably the browser needs to move the
selection or focus under normal UI commands, but the add-on
technology needs to be cued to slew the viewport to restore that
idea that the selection/focus is in view.  I am extrapolating
from the Lynx behavior as regards a text find in the current
document, where the displayed region is slewed to include the
first hit and if it is a clickable it becomes the focused
element.

I was probably confusing selection and focus in some of my
discussion earlier today.  In terms of isolating the text in a
table cell, it could be done by establishing that document
subtree as current selection and keying presentation style to
selection in such a way that the screen reader would complete the
reading of a multiline cell without digressing into the rest of
the page.

I am not sure that "point of regard" is a sufficiently well
defined concept to be used to construct guidelines.  It has been
used in ways that mix the idea of a true point with this viewport
or peephole.

Note that what one can select with the mouse is often not limited
to the HTML-declared set of entities, but involves arbitrary text
or pixel ranges that are within the currently displayed portion
of the document [or sub-object] canvas.  Similarly, there may be
the option to press a button for any cell in the Braille display,
not just HTML-level entities.
   
Quote for reference.

  2.3 Views, Point of Regard, Selection, Focus, and Events
  
    Views and viewports
    
   User agents may handle different types of source information:
   documents, sound objects, video objects, etc. The user The user
   perceives the information through a viewport, which may be a window,
   frame, a piece of paper, a speaker, a virtual magnifying glass, etc. A
   viewport may contain another viewport (e.g., nested frames, plug-ins,
   etc.).
   
   User agents may render the same source information in a variety of
   ways; each rendering is called a view. For instance, a user agent may
   allow users to view a document in one window and a generated list of
   headers for the document in another.
   
   The view is how source information is rendered and the viewport is
   where it is rendered.
   
   Generally, viewports give users access to all rendered information,
   though not always at once. For example, a video player shows a certain
   number of frames per second, but allows the user to rewind and fast
   forward. A visual browser viewport generally features scrollbars or
   some other paging mechanism that allows the user to bring the rendered
   content into view.
   
    Point of regard, Selection, and Focus
    
   Some of the guidelines below involve tracking the user's point of
   regard in the view. The point of regard describes where the user is
   expected to interact with the rendered information. As the guidelines
   below state, user agents should avoid displacing the viewport away
   from the user's point of regard as this can disorient users.
   
   Identifying the point of regard depends on the viewport. For paper,
   for example, it is difficult to identify the point of regard any more
   precisely than on the entire page. For sound and audio players (and
   linear devices in general), the point of regard designates the
   information currently being rendered.
   
   When the viewport gives the user access to information in more than
   one dimension (e.g., on the screen), there are several mechanisms
   generally offered by user agents that may be used to identify the
   point of regard:
   
   The insertion point.
          The insertion point is the location where document editing
          takes place. The insertion point may is set by the user (e.g.,
          by a pointing device or the keyboard editing keys) or through
          an application programming interface (API). A view may have
          only one insertion point. When several views co-exist, each may
          have an insertion point, but only one is active, called the
          current insertion point
          
          The insertion point is generally rendered specially (e.g., on
          the screen, by a vertical bar or similar cursor).
          
   The user focus.
          The user focus designates an active component in a document. In
          HTML documents, active components are defined to be links, form
          controls, elements with a value for the "longdesc" attribute,
          and elements with associated scripts. An element with the focus
          may be activated through any number of mechanisms, including
          the mouse, keyboard, an API, etc. The meaning of activation
          depends on the component. For instance, when a link is
          activated, the user agent generally retrieves the linked
          resource, which may be another Web page, program, etc. When a
          form control is activated, it may change state (e.g., check
          boxes) or may take user input (e.g., a text field). Activating
          a component with a script assigned for that particular
          activation mechanism (e.g., mouse down event, key press event,
          etc.) causes the script to be executed.
          
          A view has only one focus. When several views co-exist, each
          may have a focus, but only one is active, called the current
          focus.
          
          The current focus is generally highlighted.
          
   The user selection
          The user selection is defined as the part of a document
          (possibly spanning several elements) identified for user
          interaction other than with active components. For instance,
          the selection may be used for cut/copy/paste operations, to
          identify what a screen reader should read, etc. The user
          selection may be set by the user (e.g., by a pointing device or
          the keyboard) or through an application programming interface
          (API). A view may have only one user selection. When several
          views co-exist, each may have a user selection, but only one is
          active, called the current user selection.
          
          The user selection is generally highlighted. On the screen, the
          selection may be highlighted using colors, fonts, graphics, or
          other mechanisms. Highlighted text is often used by third-party
          assistive technologies to indicate through speech or Braille
          output what the user wants to read. Most screen readers are
          sensitive to highlight colors. [64]Third-party assistive
          technologies may provide alternative presentation of the
          selection through speech, enlargement, or dynamic Braille
          display.
          
          The user selection may be used, for example, to identify the
          "current cell" of a table that the user is navigating.
          
   Both the current focus and the current user selection must be in the
   same view, called the current view. The current view is generally
   highlighted when several views co-exist.
   
   Which of the three mechanisms - insertion point, selection, and focus
   - is used to designate the point of regard depends on context. For
   example, for navigating among form controls, the focus determines
   which control has the point of regard. For navigating table cells, the
   selection determines which cell has the point of regard. When a
   technique involves the point of regard, it specifies which mechanism
   is used to designate it.
   
Received on Wednesday, 11 November 1998 22:07:58 GMT

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