public final String sliceFrom(int start) {
        return input.subSequence(start, position).toString();
    }
Copies a slice of the expression into a string, 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 copied slice of the expression from {@code start} to {@link #position}.
smithy-utils/src/main/java/software/amazon/smithy/utils/SimpleParser.java