An important rule regarding integer literals is that they must be written without commas. This means that when defining an integer in programming, you should write it as a continuous string of digits. For example, "1000" is acceptable, while "1,000" would not be valid in most programming languages. The rationale behind this is to ensure that the programming language can properly interpret the integer value without ambiguity. Commas are not considered valid characters in the representation of integer literals, as they are typically used in formatting for readability in text but not within code.
Regarding the other options, they suggest various forms or limitations that do not align with standard practices for integer literals in programming. The notion of limiting integer literals to single digits or capping them at a specific value, such as 100, is also not accurate, as integers can encompass a much broader range of values, depending on the data type used.