The layer names used by Xic are CIF-style alphanumeric tokens of four characters or fewer. In addition, layers can have an optional long name, which has no restrictions on length or character type. Layers can be resolved by either name.
When working with GDSII and other files that use a numeric layer/datatype combination to designate layers, the layer/datatype combinations can be mapped into arbitrary Xic layers using the mapping constructs described in 11.6. If no such mapping is found, a default name will be used.
When the layer and datatype numbers are in the range 0-255 the default name string takes the form of a four-byte upper case hexadecimal integer. The two left characters indicate the layer number, zero padded, in the range 0-255. Similarly, the two right characters represent the datatype number. For example, layer 33, datatype 15 has the name ``210F''.
Xic supports layer and datatype numbers in the range 0-65535. Although values larger than 255 are outside of the GDSII specification, they are compatible with the GDSII file format and are used as extensions in some vendor's products. To represent the case where either value is larger than 255, an eight digit hex number is used. This is analogous to the four character encoding, but each field uses four characters. The default layer name is arbitrary, but the long name is set to this encoding.
When providing a layer name of this type to Xic, an alternate ``decimal'' form can be used. This is ``layer,datatype'' where the two integers are separated by a comma (no space). Thus, ``33,15'' is an equivalent way to specify the layer name for the example above. This is a convenience for entering layer names into the input fields of files and graphical windows of Xic. Internally, the layer name is always stored as the hex name.
In some cases when working with layer/datatype combinations, one of the two fields can be a wildcard. In the hex format, the hex digits of the appropriate field can be set to ``X''. In the decimal representation, a single `-' replaces the appropriate digits. For example, ``0FXX'' and ``15,-'' equivalently specify layer number 15 and any datatype number.