Short answer. The Civil Code's provisions on co-ownership do. Article 90 of the Family Code says those rules apply to the absolute community of property between spouses "in all matters not provided for" in the Family Code chapter that governs it, so a question the marriage-property rules leave open is answered by ordinary co-ownership law instead.
What the law says
The provisions on co-ownership shall apply to the absolute community of property between the spouses in all matters not provided for in this Chapter.
Family Code, Article 90 — Co-ownership Rules Apply Suppletorily. Read the full provision →
Article 90 is a gap-filling rule
Article 90 provides that the provisions on co-ownership shall apply to the absolute community of property between the spouses in all matters not provided for in this Chapter. The Family Code chapter on absolute community sets out its own specific rules — what falls into the community, how it is administered, what it answers for — but it does not address every possible situation. Where it is silent, the general Civil Code rules on co-ownership step in rather than leaving a void.
Why the community is treated as a form of co-ownership
The absolute community regime already functions like a form of joint ownership between spouses — both generally own the community property together, without dividing it into separate shares during the marriage. Because of that structural similarity, it makes sense that unresolved questions default to the body of law already written for co-ownership generally, rather than requiring the Family Code to spell out every scenario on its own.
The Family Code uses the same technique for the other regime, pointing the conjugal partnership of gains to the rules on the contract of partnership for matters it does not itself provide for. Each regime borrows from the body of law it most closely resembles, which is why the suppletory source differs depending on which property regime the marriage is under.
What kinds of gaps this can cover
Situations the absolute community chapter does not spell out — such as certain aspects of how co-owners deal with the property, or disputes among those with an interest in it that the Family Code chapter does not directly address — can be resolved by looking to the suppletory co-ownership rules. The key limit is the phrase "not provided for in this Chapter": where the Family Code chapter already has an answer, that answer controls, and co-ownership law only supplements what is missing.
The gap-filling also runs in one direction only, and the clearest examples are the co-ownership rules that do not carry over. An ordinary co-owner may sell his undivided share and may demand partition at almost any time; spouses under an absolute community cannot, because the Chapter deals with those matters itself — Article 89 bars a waiver of rights or interest in the community during the marriage. Where the Chapter has spoken, co-ownership law is simply not reached.
Why this matters for a specific dispute
If you and your spouse (or your spouse's estate) disagree about something the absolute-community rules do not directly settle, the answer is not automatically "there is no rule" — it may be found in the Civil Code's co-ownership provisions instead. Because working out which body of rules governs a particular point can be technical, it is worth bringing the specific facts to a lawyer rather than assuming either set of rules by default.