Some people think that using this title means that emperors knew each other at an early age, hoping for a long time, because they were only teenagers when they got married in ancient times, and now they are still in junior high school, as if they had known each other since childhood. With this title, they think they are childhood friends, which sounds reasonable, but there is no evidence to confirm this statement.
The change of catalpa may also be due to the conflict between the original two words. Because according to the original two words, they actually have the same meaning, so they may be repeated. Because many scholars think that these two words don't look very literate when writing novels, they change them into a word that looks literate. There is also a saying that these two words may change after a long time, because many people haven't read the book and don't know which two words they are.
However, the reason why the word was changed to catalpa beside the current wooden character may also be to show that the relationship between the two emperors should be very good, just like the villagers who have known each other since childhood. Because only this kind of tree grows with mulberry trees, it is often used to refer to their hometown.
Such a name may also be more because people don't understand the royal family. Although everyone likes to think that the relationship between the emperor and the queen must be very good. However, many people in ancient times never saw it before they got married, and the royal family sometimes saw it, but all kinds of literati had many beautification ideas when they created it.
However, these ideas often reflect the relationship between people and the upper class at that time. Everyone knows very little about each other, because the system was very strict at that time, and you came from a humble background, so you may not be in touch with the upper class in your life.