Based on the provided legal document, the key points are as follows:

1. An unregistered sale deed cannot be admitted into evidence for want of registration, and its contents cannot be used for any collateral purpose. This is because the legal requirement of registration is essential for the document to have evidentiary value in establishing rights or interests in immovable property (!) (!) .

2. The admissibility of a document depends on its nature, contents, and the facts and circumstances of each case. In particular, a collateral transaction should not create or extinguish rights, interests, or title in immovable property through such a document (!) .

3. Even if a sale deed is not admissible as evidence of title due to lack of registration, it may still be examined for collateral purposes, such as understanding possession or other related facts. However, such collateral use is limited and cannot be employed to prove rights or interests in property that require registration (!) .

4. The court affirmed the trial court's decision to refuse the marking of the unregistered sale deed as an exhibit, emphasizing that documents inadmissible in evidence cannot be used to prove any clause or interest, especially in the context of creating or extinguishing rights in immovable property (!) .

5. The case involved a dispute where the document in question was a sale deed that was not registered, and the court held that its contents could not be employed for collateral purposes, leading to the dismissal of the revision petition (!) .

6. The legal principle underscores that registration is a mandatory requirement for conveying title and that documents not registered cannot be relied upon for establishing or extinguishing rights in immovable property, reinforcing the importance of compliance with registration laws (!) (!) .

7. The decision highlights that procedural stages, such as interlocutory decisions regarding document admissibility, should be approached with caution, and the ultimate admissibility depends on the legal requirements and the purpose for which the document is being used (!) .

8. The court also noted that the purpose of examining such documents is limited to understanding possession or factual circumstances, not to prove substantive rights or interests that require registration (!) .

These key points collectively reinforce the legal requirement that only registered sale deeds can be used as evidence to establish rights or interests in immovable property, and unregistered deeds are restricted to collateral considerations without evidentiary value for substantive rights.