Even after thorough research, sometimes someone’s parentage might be uncertain. Conventions have developed that this sort of information is useful to capture (as the proof might one day be forthcoming), but to distinguish that there isn’t enough proof to be sure. These connections are often shown on family charts with dashed or dotted, rather than solid, lines. This can be set via the “Certainty” box on the “Families” tab, of the “Current Person Other Detail” dialog, accessed from the ⋮ button, located next to the name field.
In the example above, the “Family As Child” certainty has been set to possible, and so the connection between Peter and his parents is shown with a dashed line, rather than a solid line.