Shared Facts are another term for "Marrage Facts".
FTM does not support the ASSO construct found in GEDCOM which is used to ASSOciate two individuals.
The ASSO construct or structure is similar to a fact but is not part of the fact construct. It does give the user the ability to:
1) Provide a relationship type
2) Provide a source_citation
3) Enter NOTES
Also FTM does not provide as part of the BIRTh and ADOPtion fact the ability to directly link the fact to a FAMily unit. This is also part of the GEDCOM standard, which also allows for indicating the FAMily unit that the BIRTh event was associated with or the FAMily the individual was adopted into AND which or both of the parents of that family unit.