Identifiers are used as names for classes, variables, constants and routines. Identifiers are strings that consist only of letters, digits and the underscore (_), where the first character is a letter or an underscore.
Example of legal identifiers are:
abc
Num23
addAtEnd
add_at_beginning
_count
Examples of illegal identifiers are
hit cnt - - error: space in identifier
23add - - error: digit at start of identifier
#elem - - error: illegal symbol (#) in identifier
Blue identifiers are case sensitive. That means that abc and ABC are two different identifiers.
By convention, class names are often written with a leading capital, whereas routine names start with a lowercase character.