Validation and Substitution:
Validations and substitutions are used to check the conditions while posting a document in sap system.
The step of Validation is.
1) Prerequisites
2) Step
3) Message
Setting up the FI Validations:
http://www.sap-basis-abap.com/sapfi004.htm
https://websmp104.sap-ag.de/~form/handler?_APP=01100107900000000342&_EVENT=REDIR&_NNUM=842318
https://websmp104.sap-ag.de/~form/handler?_APP=01100107900000000342&_EVENT=REDIR&_NNUM=42615
Substitution:
Substitution permits the customer-specific enhancement (substitution) of certain field contents.
Substitution consists of several steps (up to 999 are possible), each with two parts:
. Prerequisite
. Replacement
Substitutions are not supported by the document parking feature. Substitutions can only be made with posting transactions after turning parked documents into accounting documents.