All attributes and pseudo-attributes may be recognised within expressions. Optionally they may be followed by ’OF’ to denote a different element to the current one; e.g. POS OF /VESS1. Brackets may be used to denote an element of an array, for example DESP[8 + 1] for the ninth value of DESP. Since syntax clashes are possible, the keyword ATTRIB may be used to denote that an attribute follows. For example, ATTRIB E will denote the pseudo-attribute EAST as opposed to the start of a position or direction. Attributes are described in the Data Model Reference Manual.