Mr. Simmons is one of the sharper experts here, but he opted out becuase I could give you a little bit better information.
In its effort to make the court process more accessible to the public, the California Judicial Council created certain standarized forms. The "FL" forms are those forms pertaining to matters brought in the family law courts.
"FL-300" is the standard notice and Order to Show Cause, or "OSC" for short. An OSC is a request for the court to contemplate general family law matters. Functionally, it works the same as a motion in most every way. In short, once a petition has been made, this is the form that actually gets the substance of the petition before the court.
"FL-310" is the application for the FL-300. The FL-310 specifies the particulars asked for the in FL-300. So, for example, if you are noticing and requesting a change in spousal support via the FL-300, the FL-310 lets the court know what you would like the change to be made to and the factual and legal basis for the change. When filing with the court, the FL-310 always accompanies the FL-300.
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