An identifier is a string of letters, numbers, and underscores (_), used to name and identify following entities:
A identifier must begin with a letter or underscore and must not contain spaces. National characters (accented characters) are not allowed in identifiers. Upper/lower case is not relevant.
Example:
IW215, QX75, IDENT, LIM_SW_5, abcd, ab_cd, _MAIN, _12V7