Property Registration Decree (PD 1529)
Section 25. Opposition to application in ordinary proceedings. Any person claiming an interest, whether named in the notice or not, may appear and file an opposition on or before the date of initial hearing, or within such further time as may be allowed by the court. The opposition shall state all the objections to the application and shall set forth the interest claimed by the party filing the same and apply for the remedy desired, and shall be signed and sworn to by him or by some other duly authorized person.
If the opposition or the adverse claim of any person covers only a portion of the lot and said portion is not properly delimited on the plan attached to the application, or in case of undivided co-ownership, conflicting claims of ownership or possession, or overlapping of boundaries, the court may require the parties to submit a subdivision plan duly approved by the Director of Lands.