FIND('=><')

To make a bit easier to explain let's assume the statement was Rec.FIND('=><).

It's asking the system to first find the record that has the same value(s) as the primary key field(s) of Rec. It's like Rec.GET(...), but them within the filters applied to Rec.
If it cannot find this record the system should return the record that logically directly follows this record (that could not be found).
If no following can be found the system should return the record that directly logically precedes it.

You could mimic this by the following code:

IF NOT Rec.FIND('=') THEN
  IF NOT Rec.FIND('>') THEN
    Rec.FIND('<');

But of course Rec.FIND('=><) is only one call to the server.