Tag <INPUT> - http://www.w3schools.com/tags/tag_input.asp
Example:
<input type="file" name="file" accept="list_of_mime_types">
list_of_mime_types : A comma-separated list of MIME types that indicates the MIME type of the file transfer
MIME Types - http://www.w3schools.com/media/media_mimeref.asp
Example:
*.txt => text/plain
Felissa