IDENTIFIER
The basic unquoted identifier token. Starts with a letter or underscore, followed by zero or more letters, digits, or underscores. Case-sensitive. Reserved words cannot appear as plain identifiers; use a delimited or quoted form instead.
Examples
Simple identifier
Patient
Camel-case identifier
birthDate
Underscore prefix
_privateVar
EBNF
IDENTIFIER : ([A-Za-z] | '_') ([A-Za-z0-9] | '_')* ;