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Re: Questions about TABLE SUMMARY element

From: Gregory J. Rosmaita <unagi69@concentric.net>
Date: Wed, 31 May 2000 02:17:58 -0400
Message-Id: <>
To: Charles McCathieNevile <charles@w3.org>
Cc: WAI Interest Group Emailing List <w3c-wai-ig@w3.org>
aloha, charles!

in a reply, posted to the WAI-IG list, you commented:

Given that the summary attribute isn't available on many of the current 
generation of browsers, you might also consider using a caption element 
instead - that is rendered by nearly everything.

while i agree that the summary attribute isn't widely supported by quote 
mainstream unquote user agents, it is supported by several assistive 
technologies (such as JFW 3.5, which reads the SUMMARY defined for a TABLE 
when it is present before attempting to articulate the content of the 
TABLE), as well as several self-voicing browsers

the question shouldn't be quote which should i use, SUMMARY or CAPTION? 
unquote, but quote why should i utilize both? unquote

the answer to why should i utilize the SUMMARY attribute is eloquently 
provided by the HTML 4.01 Recommendation [reference 1]

This attribute provides a summary of the table's purpose and structure for 
user agents rendering to non-visual media such as speech and Braille.

moreover, the HTML 4.01 Recommendation also states,

The following informative list describes what operations user agents
may carry out when rendering a table:
      * Make the table summary available to the user. Authors should
        provide a summary of a table's content and structure so that
        people using non-visual user agents may better understand it.

from which it is clear that:

a) the SUMMARY attribute is of great orientational utility to anyone 
attempting to review web content in a non-graphical slash non-visual slash 
limited visual modality, such as when using a screen reader and/or a 
refreshable braille display to access web content, or a mobile or pervasive 
device, such as a Personal Data Assistant (PDA), which doesn't have enough 
screen space to display the table in its entirety, but which could (and 
should) use the SUMMARY attribute to provide users with information about 
the table or tables contained in a page, thereby providing the user of the 
mobile device with the option to have the device render the table (in 
whatever manner it is capable of doing so) or skip it and preserve precious 
bandwidth and maximize limited processing capacities...  using a document's 
meta-data is far more accurate and intelligent an approach to providing the 
user with information in a form that is immediately useful to him or her, 
than is relying upon summarizing software to give the mobile device user a 
sense of the contents of a web page before the entire page, or parts 
thereof, are downloaded to the device, which really blurs the line between 
human and machine readable, but that's a thread from another list...

b) the SUMMARY attribute (unlike the CAPTION element) is not intended to be 
rendered by quote mainstream graphical user agents unquote

as regards the CAPTION element, the HTML 4.01 Recommendation states:

    When present, the CAPTION element's text should describe the nature of
    the table. The CAPTION element is only permitted immediately after the
    TABLE start tag. A TABLE element may only contain one CAPTION element.

    Visual user agents allow sighted people to quickly grasp the structure
    of the table from the headings as well as the caption. A consequence
    of this is that captions will often be inadequate as a summary of the
    purpose and structure of the table from the perspective of people
    relying on non-visual user agents.

    Authors should therefore take care to provide additional information
    summarizing the purpose and structure of the table using the summary
    attribute of the TABLE element. This is especially important for
    tables without captions. Examples below illustrate the use of the
    summary attribute.

    Visual user agents should avoid clipping any part of the table
    including the caption, unless a means is provided to access all parts,
    e.g., by horizontal or vertical scrolling. We recommend that the
    caption text be wrapped to the same width as the table. (See also the
    section on recommended layout algorithms.)

in summary, when defining a TABLE, one shouldn't choose between CAPTION and 
SUMMARY, as they are intended to serve 2 entirely different, yet 
inter-related, functionalities...  authors, should be encouraged to use 
SUMMARY, as it (1) was explicitly defined as an accessibility aid; and (2) 
it provides someone who (for whatever reason) cannot see the table (in part 
or in whole) with a narrative equivalent of what the visually oriented 
layout that comprises a data table communicates to a user who is capable of 
perceiving the table in its entirety -- namely the relationships between 
disparate pieces of data, accorded by their position in relation to one 

even if one is using tables for layout purposes (something i neither 
condone, nor recommend, nor condemn utterly), one should utilize a summary, 
as it helps to re-orient the user in the face of an abrupt paradigm shift 
-- at least, that is, those fortunate enough to have access to adaptive 
technology or a targeted user agent that is capable of traversing tables 
according to their structural elements -- for example, if a nested table is 
used to create a sidebar containing supplemental links or a captioned 
photo, the function and purpose of the nested table should clearly be 
indicated to the user via the SUMMARY attribute, as in:

         SUMMARY="Sidebar Containing Supplemental Links"
         SUMMARY="Photograph and Caption"

so that when focus is serially received by the nested layout table -- as 
when a page is voiced using JFW or by emacspeak, in conjunction with the w3 
browser, which has the decided advantage of supporting the aural styling 
rules of CSS2 [reference 2], so that the end of the nested table can also 
be aurally indicated using a client-side stylesheet -- the purpose of that 
subordinate table is clarified...

and, of course, users should always be able to turn off support for SUMMARY 
if they like, but it does need to be supported, and it does need to be 
implemented -- as widely and often as possible


[1] http://www.w3.org/TR/html401/struct/tables.html#adef-summary
[2] http://www.w3.org/TR/REC-CSS2/aural.html
Received on Wednesday, 31 May 2000 02:20:10 UTC

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