According to Art. 108 EPC a notice of appeal shall be filed in accordance with the Implementing Regulations, at the EPO within two months after the date of notification of the decision. Notice of appeal shall not be deemed to have been filed until the fee for appeal has been paid. The content of the notice of appeal is set out in R. 99 EPC. In view of the future use of electronic means of communication, it was found useful to avoid references to 'in writing' or 'in written form' and leave such regulation to the Implementing Regulations.
The admissibility of an appeal can only be assessed as a whole (T 382/96, T 1763/06, T 509/07, T 23/10, T 2001/14). There is no support in the EPC for a notion of 'partial admissibility' of an appeal (T 774/97, T 509/07).
See also chapter V.A.9.3. "Appeal deemed not to have been filed or inadmissible appeal".