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:
Royal_Institute_of_British_Architects

Context:
The Royal Institute of British Architects (RIBA) is a professional body for architects primarily in the United Kingdom, but also internationally, founded for the advancement of architecture under its charter granted in 1837 and Supplemental Charter granted in 1971.

Question:
When was RIBA's founding document expanded?

1971