Some string expressions such as $substr, $substrBytes, $substrCP, $strcasecmp, $toLower and $toUpper will coerce their inputs to a string, allowing numbers, code, etc. to be converted as input. Others, such as $strLenBytes and $strLenCP will only allow string inputs, resulting in an error on any other input. Still others, such as $trim, $rtrim, $ltrim, $indexOfBytes, $indexOfCP, $split, and $concat will return null on any nullish input, and only accept strings otherwise.

We need to decide which of these behaviors is most useful and most consistent, and update the others to be consistent.