An attribute is represented by a single cell.
The first element of the cell references the attribute key, the second value the corresponding value.
:::{="syntax"}
__AttributeKeyValue__ **=** ''('' __AttributeKey__ ''.'' __AttributeValue__ '')''.
:::
__AttributeKey__ and __AttributeValue__ are [[string values|00001012930500]].

An empty key denotes the generic attribute.

A key with the value ''"-"'' specifies the default attribute.
In this case, the attribute value is not interpreted.

Some examples:
* ''()'' represents the absence of attributes,
* ''(("-" . ""))'' represent the default attribute,
* ''(("-" . "") ("" . "syntax"))'' adds the generic attribute with the value ""syntax"",
* ''(("lang" . "en"))'' denotes the attribute key ""lang"" with a value ""en"".