Clicking a character in the Alphabetical index will display a list of the names that start with the character you clicked.
The second to last item in the Alphabetical index can be (unknown). This entry will be present when there are people in the database whose surname has not been recorded or does not contain any characters from the supported languages. Unknown surnames are often recorded as ?, and these "names" will be recognized as (unknown). This will also happen if the person is unknown.
Note: Surnames entered as, for example, Nn, NN, Unknown, or even N.N. will not be found in the (unknown) list. Instead, you will find these persons by clicking N or U because these are the initial letters of those "names". PhpGedView cannot possibly account for all possible ways of entering unknown surnames; there is no recognized convention for this.
At the end of the Alphabetical index you see ALL. When you click on this item, you will see a list of all surnames in the database.
Missing characters If your Alphabetical index appears to be incomplete, with missing letters, your database doesn't contain any surnames that start with that missing letter.