Break the block below (topic "{topic}") into its SUBBLOCKS — the individual learnable sub-points — and extract per subblock the learning facts from the material. A later guide writes a short text PER subblock; the facts are the binding basis for guide text, levels, and exam questions — they must be **correct**.

BLOCK:
{block}

{source}

What a subblock is:
- A single sub-point you must learn for the block. One statement, one aspect, one pitfall.
- Examples: block `<img>` → `src` (Bildquelle), `alt` (Alternativtext), empty `alt` for decorative images. Block `<p>` → text paragraph as a block, allowed inline children, no nesting.

DECISIVE — the count follows the difficulty:
- A simple, trivial block has FEW subblocks (1–2). Do NOT inflate it.
- A complex, rich block has MANY subblocks. Leave out nothing essential the material covers.
- Each subblock is atomic (one sub-point), backed by the excerpts — a point the excerpts do not support is left out.
- Subblock titles in GERMAN (code identifiers stay original), max. ~10 words, one statement.
{seeds}
Per subblock, collect ONLY the essentials (all field content in GERMAN; technical terms/code identifiers stay original):
- **level**: beginner | advanced | expert — difficulty within this block.
- **relevance**: relevant (core of the topic) | peripheral (edge knowledge).
- **key_points**: 1–3 concise statements — what must one understand?
- **prerequisites**: what must one know beforehand (a half-sentence)? Empty if nothing.
- **hurdles**: typical beginner misconception (a half-sentence). Empty if none.
- **cited_facts**: hard facts (definitions, formulas, values, names) — **only what the excerpts back**, each with the location (e.g. „Skript Def. 6.3, Z.66"). Invent no values, compute nothing yourself.
- **example_idea**: ONE example that carries understanding — freely phrased. Empty if an example adds nothing.

HARD SEPARATION: `cited_facts` = only backable material. A worked example, an invented sentence, a constructed case → `example_idea`, NEVER `cited_facts`. When in doubt: better to leave out than to claim falsely.

Reply with ONLY the JSON as your final message — no code fences, no other text. EXACTLY this format:
{{"subs": [
  {{"title": "…", "level": "beginner|advanced|expert", "relevance": "relevant|peripheral",
    "key_points": ["…"], "prerequisites": "…", "hurdles": "…",
    "cited_facts": [{{"text": "…", "source": "…"}}], "example_idea": "…"}}
]}}
{extra}