code: public StringExpression substring(int beginIndex) {
          return Expressions.stringOperation(Ops.SUBSTR_1ARG, mixin, ConstantImpl.create(beginIndex));
      }
docs: Create a {@code this.substring(beginIndex)} expression
  
  @param beginIndex inclusive start index
  @return this.substring(beginIndex)
  @see java.lang.String#substring(int)