+,-(Plus sign, minus sign) is a number type? (In SQL Server 2000)

After debugging the stored procedure today, we found a strange problem. We all know that the function isnumeric is used to determine whether the expression is a valid numeric type, but the result I got with isnumeric ('+') is 1, that is, + is a number type. Then I tried to subtract the number-it also got the same result, I was puzzled. Later I thought that if they were numbers, what would they be? I converted them to convert (INT, '+') and the result was 0, convert (INT, '-') returns zero. It's strange. Why is it like this? This is not described in the online help of SQL Server. Later I tried other operators. Except for the plus sign and minus sign, none of the other operators are numerical (or, I have not found). Is this a bug in SQL Server2000? (Maybe this is not a problem at all)
You can run the following in the SQL Server Query Analyzer:
Print (isnumeric ('+ '))
Print (isnumeric ('-'))
Print (convert (INT, '+ '))
Print (convert (INT ,'-'))
The result is:
1
1
0
0