CSS in Action
Invisible Content Just for Screen Reader Users
There are occasional instances where content should be made available to screen reader users, but hidden from sighted users. In most cases, if content (particularly content that provides functionality or interactivity) is important enough to provide to screen reader users, it should probably be made available to all users. Cases where verbose cues or instructions are provided only for screen reader users are most likely a reflection of poor design and accessibility. However, there are a few cases where information is apparent visually, but may not be apparent to screen reader users. In these cases, it may be appropriate to mark-up content in a way that it is read by a screen reader, but invisible to sighted users.
Techniques for hiding text
There are several mechanisms that can be used for hiding content. It's important that a technique be implemented that results in the desired outcome and accessibility.
These styles will hide text from all users. The text is removed from the visual flow of the page and is ignored by screen readers. Do not use this CSS if you want the content to be read by a screen reader. But DO use it for content you don't want read by screen readers.
height:0px or other 0 pixel sizing techniques
As above, because an element with no height or width is removed from the flow of the page, most screen readers will ignore this content. HTML width and height may give the same result. Do not size content to 0 pixels if you want the content to be read by a screen reader. Content styled with
line-height:0 may work, though the elements would still take horizontal space on the screen. All of these techniques may result in search engine penalties as they may interpreted to be malicious.
This approach moves the content to the left 10000 pixels - thus off the visible screen. Screen readers will still read text with this style. However, if a link or form element is given this style, it may result in a focus indicator (the dotted lines or 'marching ants' that surround a focused link) that extends from where the element should be located in the page to the place it is actually located (way to the left). This is not very pretty. This approach also causes issues in right-to-left languages. As such, this approach may be a viable option if the element does not contain navigable elements, though better techniques are available.
Absolutely positioning content off-screen
Using CSS to move hidden elements to a position off-screen is generally accepted as an accessible method of hiding content visually. The following are the recommended styles for visually hiding content that will be read by a screen reader.
The .hidden CSS class should then be referenced from within the tag of the element being hidden, as shown:
<div class="hidden">This text is hidden.</div>
Sighted users will not see the hidden content at all. It will be out of their viewing range - hidden well to the left of the visible browser window. Screen reader users will have access to the content as if it were not hidden at all. Screen readers read the content normally, completely ignoring the styles used in this technique.
Let's analyze the styles in detail.
position:absolute; tells the browser to remove the element from the page flow and to begin positioning it.
left:-10000px; moves the content 10000 pixels to the left.
top:auto; tells the browser to position the content vertically at the same location it was originally. Omitting
top may result in the
left style being ignored in some instances and browsers. In short, this part of the code moves the element 10000 pixels straight to the left.
width:1px; height:1px; overflow:hidden; tells the browser to make the element 1px by 1px in size and to visually hide everything that does not fit into these dimensions. While this is a likely a little overkill and can probably be omitted in most circumstances, there are a few instances where positioning may be disabled, but all other styles remain enabled. In this case, the element will remain in its original position, but will only take 1 pixel of space.
It is sometimes recommended to position content using
left:0px; top:-500px (or similar). While this works by positioning the content above the top of the page, if the hidden element contains a link or form element, upon receiving keyboard focus, the browser attempts to scroll to the element - thus scrolling the browser to the top of the page. This could result in confusion for sighted keyboard users. By positioning directly to the left, the browser will not scroll to the top of the page. It should be noted that because links and form elements provide functionality, they should rarely be hidden from sighted users. Sighted users will not be able to see which element currently has focus because it is hidden off-screen.
clip: rect(1px, 1px, 1px, 1px);
A fairly modern technique of using CSS to hide or clip content that does not fit into a 1 pixel visible area will essentially hide the content visibly, but still allow it to be read by modern screen readers.
In general, content should only be hidden from sighted users and made available to screen reader users when content is apparent visually, but not apparent to screen reader users.
Instructional cues and indicators
This technique can be used to provide instructional cues and indicators to screen reader users. This should be implemented with discretion and only where necessary. This page demonstrates proper use of this technique in two places.
First, the search text box at the top of the page has a hidden label immediately before it. It is apparent visually that the text box is for searching due to the presentation and the search button, but a screen reader requires a label for the text field. As such, we provided a label, but have hidden it visually.
Second, the breadcrumbs at the top of the page are a common design convention. Most web users understand the convention and can identify breadcrumbs visually. Because a screen reader accesses the breadcrumb links and content linearly, it may not be apparent to them that it is breadcrumbs until they have read a portion of it. As such, we have added hidden text of "You are here:" just prior to the breadcrumbs.
You can see all of this hidden text by disabling styles for this page. Remember, all content hidden visually with CSS will become visible if styles are disabled.
Form controls are sometimes presented visually so that text is visually associated as the label for multiple controls. Consider data entry where one "First name" text might describe the function of multiple text boxes that appear below it. Sometimes tables are used for these presentations. Alternatively, sometimes one control may be labeled by multiple items of text, such as a password field that is preceded by the word "Password:" and followed by the word "Required". Using standard form labelling, there is no way to associate one text item to multiple controls or multiple texts to one form control. In these case, the appropriate labels could be provided in the markup adjacent to their respective form elements, but hidden using the CSS above.
A common example of this is when two or more text input elements are used for phone numbers.
Most visual users in North America will understand that the individual text input areas correspond to the different sections of standard phone numbers. Screen reader users, however, may attempt to enter the entire phone number in the first box. Confusion is likely when they discover that the box limits them to only 3 characters or that there are additional unlabeled text boxes that follow.
The most obvious workaround for this particular problem would be to combine all of the text input boxes into a single text input box, and then provide the appropriate label. However, off-screen labels for each distinct text box will also ensure accessibility.
<label for="area" class="hidden">Area code</label>
<input name="area" id="area" type="text" size="3" maxlength="3">
The off-screen labels would, in this case, provide an adequate description for screen reader users.
In the example above, the
title attribute could also be used to provide this information. Information in the
title attribute will be read by screen readers when a label is not present. Additionally,
aria-labelledby could be used to provide multiple labels per input or multiple inputs per label.
When the CSS techniques presented here are used to hide content, sighted users will never know that the content is there at all (unless they disable styles). Screen reader users, on the other hand, will never realize that this content is invisible to sighted users. Both kinds of users will be able to use the content intuitively, without having to adjust for either too much or too little information in the markup. This can provide important contextual cues that are otherwise impossible for screen reader users to grasp because of the visual nature of these cues. When used judiciously, this technique can resolve some of the tension between the demands of accessibility and the demands of visual design. It is not the only technique or method of solving this problem, but it is one that web developers can add to their list of possible solutions when the need arises.