You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Treaty

Context:
A treaty is an official, express written agreement that states use to legally bind themselves. A treaty is the official document which expresses that agreement in words; and it is also the objective outcome of a ceremonial occasion which acknowledges the parties and their defined relationships.

Question:
How are states that enter into a treaty bound?

legally