https://docs.splunk.com/Documentation/Splunk/8.1.0/SearchReference/ConversionFunctions#tostring.28X.2CY.
The tostring function in the eval command converts a numeric value to a string value. It can take an optional second argument that specifies the format of the string value. Some of the possible formats are:
* hex: converts the numeric value to a hexadecimal string.
* commas: adds commas to separate thousands in the numeric value.
* duration: converts the numeric value to a human-readable duration string, such as "2h 3m 4s".
Therefore, the formats A, B, and D can be used with the tostring function.