Need help in understanding the expression, pardon my ignorance
Doubt is normally replace function should replace any character provided but in the result it is just splitting single line into 2 lines.
can you please let me know what exactly it is replacing.
The above expression uses zero-width positive lookahead and lookbehind. So, this replaces zero-width between comma and string which is matched "\d+,\w+(\r?\n|$)" with linbreak.