Please answer the following question: Given the following passage  "The original Latin word "universitas" refers in general to "a number of persons associated into one body, a society, company, community, guild, corporation, etc." At the time of the emergence of urban town life and medieval guilds, specialised "associations of students and teachers with collective legal rights usually guaranteed by charters issued by princes, prelates, or the towns in which they were located" came to be denominated by this general term. Like other guilds, they were self-regulating and determined the qualifications of their members.",  answer the following question. Note that the answer is present within the text.  Question: What gave the guilds their protection of their privileges that could not be denied?
Answer:
charters