The event occurs when an file was selected on a fileImport control. The import function will detect if the file is using a comma or a semicolon as separator. Brixxbox will therefore count the occurrences of commas and semicolons in the first line (Header) and will use the higher counted char as separator.
You can access eventArgs.details inside this event to get the file content and meta data:
eventArgs.details.csvLines - Array of all lines splitted by csv rules
eventArgs.details.lines - Array of all lines splitted by csv rules
eventArgs.details.fileExtension - extension of the import file ("csv" for example)
eventArgs.details.fileExtensionLower - extension of the import file in lowercase