Problem:
Placeholder text is not “visible” to a screenreader
Solution:
This can be corrected by using the “aria-label” attribute. For this input field, the code would appear as:
<input id="table-filter" class="span12" type="text" name="privilegeFilterText" placeholder="Entity name" aria-label="enter entity name">
For a longer description the ARIA attribute "aria-describedby" could be used. See the example on page 7.
Note: I found this area of the site confusing regarding the function of the filter and other options. You could also add text to an id associated with “aria-describedby” that explains how the options in this section operate.