Solution : https://service.sap.com/sap/support/notes/327220 (SAP Service marketplace login required)
Summary : 
      This SAP Note elucidates the "Maintain: Requirements and Formulas" (VOFM) function within the R/3 Standard System, delineating its roles, related objects, and boundaries. It provides a detailed manual on how VOFM functions, including definitions, application scopes, and detailed technical instructions for its deployment, such as namespaces, object registration, and error troubleshooting detailed in chapter 2.7. The VOFM objects' structure, including ABAP form routines and TFRM/TFRMT table entries, and the process for VOFM object calls and maintenance are also covered. Importantly, distinctions are made between behavior in Standard Core and industry solutions, directing users to additional resources for specific VOFM functionalities.
Key words : 
number range customer    fofu      subsequent functions               900 - 999    pstk       group key routines                   50 - 99    tdat      data transfer routines, sales activities  pbek requirements account determination  chrg requirements batches   reak archiving, - language key    [spras]   - group indicator  [grpze]  - group number     [grpno]   - description      [bezei]examples, - group indicator            [grpze]  - group number                [grpno]  - routine 'active' indicator  [aktiv_tfrm]  - application                [kappl]   - date, grpze grpne aktiv_tfrm kappl gndat gnzei            pbed 001, spras  grpze  grpno  bezei, order   pbed requirements pricing   casc data transfer, abap form routine   =>  tfrm table entry   =>  tfrmt table entry 2, system displays message tk 112 'edit objects separately, work variable   frm_kondi_wert-nr = xkomv-kofrm
Related Notes : 
       
| 1236911 | Customer-specific copy. req. RV45B602 deleted during upgrade | 
| 1170000 | VOFM: Problems when copying formulas with enhancements | 
| 751441 | Consulting: Settings for texts from purchase order | 
| 748208 | No VAT registr. no. f EU countries - supplement Note 158890 | 
| 733924 | Sales tax, transitional rules for accession countries | 
| 614545 | RV80HGEN activates inactive formulas | 
| 598475 | XPRA RV80HGEN when transporting VOFM objects | 
| 594229 | 'Orginal System' for VOFM objects | 
| 458361 | Customizing correction in/for pricing procedure WTY | 
| 393012 | VOFM: Syntax error for user-defined routines | 
| 385067 | Various problems with VOFM functions in Release 4.6C | 
| 381348 | Using user exit, customer exit, VOFM in SD | 
| 356737 | Customer name range for VOFM routines | 
| 326560 | Various problems when using VOFM functions | 
| 28683 | PERFORM_NOT_FOUND: VOFM routine is not active | 
| 22808 | Transferring formulas |