code: public BooleanExpression contains(Expression<String> str) {
          return Expressions.booleanOperation(Ops.STRING_CONTAINS, mixin, str);
      }
docs: Create a {@code this.contains(str)} expression
  
  <p>Returns true if the given String is contained</p>
  
  @param str string
  @return this.contains(str)
  @see java.lang.String#contains(CharSequence)