private void ws() {
        while (!eof()) {
            switch (peek()) {
                case ' ':
                case '\t':
                case '\r':
                case '\n':
                    skip();
                    break;
                default:
                    return;
            }
        }
    }
Gets a slice of the expression starting from the given 0-based
character position, read all the way through to the current
position of the parser.

@param start Position to slice from, ending at the current position.
@return Returns the slice of the expression from {@code start} to {@link #position}.
smithy-jmespath/src/main/java/software/amazon/smithy/jmespath/Lexer.java