Block level help text for form controls.

Associating help text with form controls

Help text should be explicitly associated with the form control it relates to using the aria-describedby attribute. This will ensure that assistive technologies – such as screen readers – will announce this help text when the user focuses or enters the control.

A block of help text that breaks onto a new line and may extend beyond one line.
<label class="sr-only" for="inputHelpBlock">Input with help text</label>
<input type="text" id="inputHelpBlock" class="form-control" aria-describedby="helpBlock">
...
<span id="helpBlock" class="help-block">A block of help text that breaks onto a new line and may extend beyond one line.</span>

Related classes: