DLM$ is a system function (as of 4.2) which dynamically redimensions the array in a str2mat statement. In the following example, the array zzz$ will be redimensioned dynamically.
str2mat(xxx$, mat zzz$, DLM$)
The default delimiter will be to search for the following combinations of newline and carriage return characters:
\n\r \r\n \n \r
When 2 of the same delimiters are used next to each other, BR honors both making an empty string for one of the array elements. If the delimiter is "", every character will be put in a separate element of the array.
mat2str(mat zzz$, str$, [, DLM$])
By default a CR (Linux) or CRLF (Windows) will be inserted as a delimiter. The delimiter will be put after every entry from the matrix including the last entry. The delimiter can be "" which would simply concatenate the array.