Editor marks space left uninscribed on the support, but expresses doubt as to whether this is the correct encoding.
A space should be used wherever there is an intentional space left on the support: i.e. a space that never contained text (vacat). To express uncertainty as to whether or not a vacat is actually present (as opposed to text erased or lost, say), a <certainty> element with a match corresponding to the parent element (i.e. the gap element) should be given a locus with a value of "name" (meaning the space element may not be correct).
Other pages describing <space>:
Other pages describing <certainty>: