Upper and lower case forms of a letter are never distinguished except within character and string constants. Most identifiers allowed by other programming languages are also acceptable to Scheme. 7.1.1 Lexical structure for a formal syntax of identifiers. Some implementations allow all identifiers, including syntactic keywords, to be used as variables. This is a compatible extension to the language, but ambiguities in the language result when the restriction is relaxed, and the ways in which these ambiguities are resolved vary between implementations.
Whitespace characters are spaces and newlines.
Whitespace is used for improved readability and as necessary to separate tokens from each other, a token being an indivisible lexical unit such as an identifier or number, but is otherwise insignificant. Whitespace may occur between any two tokens, but not within a token. Whitespace may also occur inside a string, where it is significant. The comment continues to the end of the line on which the semicolon appears. Comments are invisible to Scheme, but the end of the line is visible as whitespace.