From what I understand, the
Chris Coyier sets out some example situations though in this blog post, but an important quote is below (in case the post goes down).
Here are some things to know about indeterminate checkboxes:
You can't make a checkbox indeterminate through HTML. There is no
indeterminate attribute. It is a property of checkboxes though, which
I should imagine you could probably use
Drupal.settings to your advantage here though, and run the check server-side for "true for some children", and pass an array of ID's through to
Drupal.settings. Following that run something like the following in a Drupal behaviour:
// This is an array of IDs
trueForSomeChildren = Drupal.settings.myModule.trueForSomeChildren;
$(trueForSomeChildrenjoin(', ')).attr("indeterminate", true);
Howeverm I don't think there's an already-built module to do what you want. There is a patch here for the FacetAPI where they allow for
indeterminate, but it kind of follows this example.