tabindex is used to define a
sequence that users follow when they use the Tab key to navigate through a
page. By default, the natural tabbing order will match the source order in
the markup. In certain circumstances it may be necessary to override the
default tabbing order, but it’s strongly recommended that you craft a page
in a logical flow and let the browser work through it in the default
order—an approach that negates the need for the
tabindex can start at 0 and
increment in any value. As such, the sequence 1, 2, 3, 4, 5 would be fine,
as would 10, 20, 30, 40, 50. If you need to introduce a
tabindex, it’s advisable to use a sequence that
contains intervals (like the second example provided), as this will give
you the opportunity to inject other controls later if need be (for
example, 10, 15, 20) without having to reindex all the
tabindex values on the page. Should a given
tabindex value be applied to more than one element
(e.g. all links in one section given a
"1", and sidebar links given a
"2"), the tabbing
order of those affected elements will be as per the source markup order.
Many people will choose to use this approach rather than a sequence with a
defined interval, such as 5, 10, 15, because it allows for additional
links or form controls to be added without the headache of re-numbering.
If a tabindex of
"-1" is used, the element it’s applied
to will no longer be keyboard focusable.
tabindex is set anywhere on a
page—even if it’s the hundredth link or the fiftieth form control—the tab
order will start at the element with the lowest
tabindex value, and work through the increments.
Only then will the tab order take in the remaining elements for
tabindex has been set. As such, great care
must be taken to ensure that adding a
doesn’t harm the usability of the page as a whole.
This code sets the
tabindex for both form controls:
<object data="giant-dog.jpg" height="225" tabindex="1"></object>
This attribute takes a number value.
Whether you would be
able to use the tab key (or equivalent) to access the
object would largely depend on the nature of the
content displayed in the
object tag. Using the simple
image example shown above, only Firefox and Opera allow the user to make
use of the
tabindex attribute in this context (in
almost all other cases—namely form controls and links—the
tabindex has excellent
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