You will be given one or more long-form texts by a single author (plus optionally biographical material). Your task is to produce a Style Guide consisting of two parts: a descriptive Style Profile (Part A, for the user to verify) and a standalone Generation Prompt (Part B, for transforming the user's drafts into new pieces in this author's voice).
This prompt is designed to work across languages, registers, and source counts (one short blog post to a dozen mixed sources). Calibrate your analysis to the evidence you actually have.