Yeah, it's one of the Big Things of their clan. Their fricking Sublime Ancestor even goes around checking if it's upheld.
"It is not the commotion which troubles me, this is a training hall," her father said mildly.
Gu Xiulan remained as she was, head bowed, hands clasped. She could tell he was not done. Zheng Nan turned to face her father as well, his expression guileless.
"It is not, however, a proper place for a spar with guests," her father continued, turning his eyes to Zheng Nan.
"Ah well, my curiosity got the better of me," he chuckled. "Your daughter is really loud, you know."
Gu Xiulan felt sweat beading on the back of her neck as the temperature in the room crept upward. She chanced a glance upward, and found her fathers face impassive and cold.
"Nonetheless, son of Zhi, I have broken your fast, given to you my wine, will you skulk in my cellars and thieve from my pantry?"
Zheng Nan's easy smile dropped away and he straightened up, losing his slouching posture. "I've done no such thing."
"Yet here you stand, in a part of my palace reserved for kin alone," her father replied. "I forgive this, for surely you were only lost in your wandering."
[...]
"How did you so quickly shame him?" she asked curiously, trying not to look at the way the wall behind where Zheng Nan had stood was shimmering with heat, distorted and rippled where stone had begun to melt.
"In my youth I traveled a great deal, including the Zheng lands. There are certain privileges accorded to a formal host, by even the most rambunctious of the stone ape's kin," Father said, returning to stroking his beard as he regarded her. "The trouble is they have very exacting definitions of formal hosting, which may give them wide leeway with the uninformed. Some are honorable and hew close regardless, some are not, as with all men. Do not be fooled by their attitudes my daughter, the Zheng have traditions as strong and hidebound as any ancient clan."