There is a page in the help that describes the syntax although, as someone pointed out recently, it has a couple typos on it. The gist is as follows;
You can have multiple values separated by commas. You can also have ranges. A range will be enclosed in either brackets, parentheses, or one of each. Within the brackets/parentheses you will typically have two numbers separated by a comma. The first number is the lower limit and the second number is the upper limit. If the range is missing one of the two numbers, it is limitless in that direction. A parentheses next to the limit number means that it does not include the limit, but includes all numbers up to the limit. A bracket includes the limit value. Ok, here are some examples.
0,1,2,3 = any time the variable equals specifically 0 or 1 or 2 or 3.
(0,1) = all numbers between 0 and 1 not including 0 or 1.
[0,1) = all numbers between 0 and 1 including 0 but not including 1
[0,1],4 = all numbers between 0 and 1 including 0 and 1 and also including 4.
(0,) = any value greater than 0 but not including 0
(,4] = any value equal to or less than 4.
(,4],6,[7,8] = any value equal to or less than 4 and 6 and any number between 7 and 8 including 7 and 8.
In a similar way, you can also make multiple rows that each have the same lookup property. The ranges are easier, but multiple rows become necessary when you are using a parameter that has a value list. Bear in mind that multiple values that equal a specific lookup property row will make the table read only. That means that the table can only be used as the input table and not the output table of a double lookup.
