javascript InputTypeCheckbox indeterminate

Indicates whether a checkbox is visually represented as being neither checked nor unchecked, yet still active. This middle ground is rendered differently for different operating systems. In Windows, the checkbox is grayed out (with the checkmark still visible if it was there originally) but still active. On the Macintosh, the checkbox displays a hyphen inside the box. The indeterminate state usually means some change elsewhere on the page has likely affected the setting of the checkbox, requiring the user to verify the checkbox's setting for accuracy. An "indeterminate" checkbox is submitted with the form.