How to tell the filter views is using I'm in the process of writing a custom views filter handler. In order to learn from the existing filters, I'd like to know how I can tell which filter class views is using when I'm configuring an (exposed) filter on the GUI.
Adding an exposed view filter inserts the following (sample) code into the view output:

 &lt;div class="view view-... view-id-... view-display-id-default view-...-id-1"&gt;
    &lt;div class="view-header"&gt;
        ...
    &lt;/div&gt;

    &lt;div class="view-filters"&gt;
        &lt;form action="..." accept-charset="UTF-8" method="get" id="views-exposed-form-..."&gt;
        &lt;div&gt;
            &lt;div class="views-exposed-form"&gt;
               &lt;div class="views-exposed-widgets clear-block"&gt;
                  &lt;div class="views-exposed-widget views-widget-filter-tid"&gt;
                     &lt;label for="edit-tid"&gt;...&lt;/label&gt;
                     &lt;div class="views-widget"&gt;
                        &lt;div class="form-item" id="edit-tid-wrapper"&gt;
                           &lt;select name="tid" class="form-select" id="edit-tid" &gt;
                              &lt;option value="All"&gt;...&lt;/option&gt;...
                           &lt;/select&gt;
                        &lt;/div&gt;
                     &lt;/div&gt;
                 &lt;/div&gt;
                 &lt;div class="views-exposed-widget views-submit-button"&gt;
                    &lt;input type="submit" id="edit-submit-..." class="form-submit" /&gt;
                 ...


It is not clear, though, why you can't find out the same by simply creating a view, exposing its filter and looking up the source code. Perhaps you could explain your question better?