The content of the famous book by Mark Levine, which contains the main theoretical material on improvisation.
There is, of course, nothing about spontaneous improvisation here. The order of things is such that first what is studied is what is being studied, and then there is a performance in accordance with what was learned, if possible putting in your own emotions and feelings.
Spontaneous improvisation does not start with prior knowledge or preparation, but emotion and inner feeling; uncontrollably using the acquired baggage - be it theory, learned repertoire, music heard throughout life, literature, cinema, theater. The meager the luggage, the more limited the result. However, there is no doubt that a given feeling or emotion is the strongest trigger for spontaneous improvisation; and any change in them instantly affects a significant transformation of the result - without connection with theoretical knowledge; as in these examples:
For the sake of inner sensation, you can invent spontaneous chords, as did Keith Jarrett. The trick here is how to get out of any situation: and this just requires training :https://disk.yandex.ru/d/2_pGLqfB4X2ykQ