Some questions are still unanswered, such as the inclusion in the BCI repertoire of some characters (currently about 24) that are already encoded in the UCS (like digits, punctuation signs, spaces and some markers), but whose unification may cause problems due to the very strict graphical layouts required by the published Bliss reference guides[citation needed]. In addition, the character metrics use a specific layout where the usual baseline is not used, and the ideographic em-square is not relevant for Bliss character designs, that use additional "earth line" and "sky line" to define the composition square. Some fonts supporting the BCI repertoire are available and usable with texts encoded with private-use assignments (PUA) within the UCS.