Compile only canonical schemd fences

Parse the information string before the body

Hand the information string to parseSchematicFence before touching the body. If it returns undefined, the block is not ours — give it straight back to the host parser. If it succeeds, compile the body and surface SchematicSyntaxError.line, because swallowing a broken example only means shipping it.

const fence = parseSchematicFence(token.info);
if (!fence) return next(token);
return compileSchematic(token.text, { ...fence, mode: 'default' }).svg;

source:V "5 V" at (80, 130) #blue [type=voltage-dc]
protection:F "breaker" at (300, 130) #amber [type=breaker]
load:B "buzzer" at (560, 130) #emerald [type=buzzer]
V.positive -> F.in #blue [line]
F.out -> B.in #emerald [line]

This site compiles every versioned fence in its own test suite, which is what stops a documentation example from being decoration. Each line keeps its own corpus, and newer syntax is never backfilled into an older one.