public Builder<T> separator(final Predicate<? super T> separator) {
			_separator = requireNonNull(separator);
			return this;
		}
Set the predicate which defines {@code separator} tokens. If the given
predicate returns {@code true} for a token, it is treated as
<em>separator</em>.

@param separator the {@code separator} token
@return {@code this} builder, for method chaining
@throws NullPointerException if the {@code separator} is {@code null}
jenetics.ext/src/main/java/io/jenetics/ext/internal/util/FormulaParser.java