Functionality
The mechanism for form-based file upload was originally proposed in RFC 1867 (published November 1995), as an extension to HTML 2.0 (RFC 1866), after its publication. Form-based file upload then was incorporated in HTML 3.2, which explicitly refers to RFC 1867 for further information on form-based file upload.
HTML 4.01 does not, in itself, describe how the file-select control is supposed to work, but it does list RFC 2388 and RFC 1867 as references.
Read more about this topic: File Select