I know some other tickets have requested accessibility compliance and a I saw where the priority for this depends on how many people are asking for it. We, like others, are required to make our website accessible, so I'm adding my voice. We have a tool that helps us identify issues, so I'm including some of those here:

1. Button missing a text alternative. Buttons should always have a text label. The label can be inserted into the HTML — it does not need to be visible to pass this check. Source code below:
   <button class="dt-button DTTT_button DTTT_button_spacer" tabindex="0" aria-controls="table_1" type="button">
   <span></span>
   <span class="dt-down-arrow">▼</span>
   </button>
2. Container element is empty. Some roles are designed to contain other roles. This element has this type of role, but it doesn't contain any required-owned elements. Source code below:
   <tfoot>
   <tr style="display: none"></tr>
   </tfoot>
3. Text is clipped when resized. Visitors should be able to scale text to 200% without losing any information. Problems often arise when overflow: hidden is used to prevent text from rendering outside of a specified area. This clips the content at the edge of its container and makes the overflow invisible. Source code below (7 occurrences):
   <span class="filter-option pull-left">Nothing selected</span>

This is a "potential issue" that would be good if it were addressed by default, though I know some CSS overrides on my end could fix this one:

1. Is it clear which page element has focus from the keyboard? Source code below (18 occurrences):
   <button type="button" class="btn dropdown-toggle bs-placeholder btn-default" data-toggle="dropdown" role="button" title="Nothing selected"
   <span class="filter-option pull-left">Nothing selected</span>
   <span class="bs-caret"></span>
   </button>
   

Not on the URL mentioned in this ticket, but other places with wpDataCharts our site:

1. Field input error is not announced in full. A user should be clear about the required input for each form field. If a field is not completed correctly, then an error message should be given. This tells the user that information is missing or that the information provided is in the wrong format.
   
   Field inputs that are marked as aria-live="assertive" cause a screen reader to interrupt the user when an error occurs. Marking a field input as aria-atomic means that the screen reader announces the complete error message each time it occurs.
   
   Source code below:
   <div aria-hidden="false" aria-live="assertive" style="position: absolute; width: 1px; height: 1px; overflow: hidden; white-space: nowrap; clip: rect(1px, 1px, 1px, 1px); margin-top: -3px; opacity: 0.01;"></div>

This is probably not a full list of issues and is only A and AA, which is what we're required to be in compliance of.

Hopefully this is helpful.

Thank you Miloš!