When it refuses

Every error carries a code, a byte offset and a message. The code is the part that is the same in every implementation; the wording after it is that implementation’s own, and may be better in some languages than others.

A conforming parser stops at the first error. Recovery — reporting every error at once — is a 0.2 question and a real want, but recovery that differs between implementations is worse than none.

Every message below was produced by running a parser, not typed from the spec.

Structural errors

BMX-E001 — unterminated slot

Hi {{ name

BMX-E001 at 3: unterminated slot: no }} on this line

A slot must close on its own line. If it could span lines, an unterminated one would look exactly like an ordinary paragraph — which is the failure this rule exists to prevent.

BMX-E002 — unterminated emphasis or strong

a *bold sentence

BMX-E002 at 2: unterminated emphasis

This is the difference from markdown in one line. Markdown renders that as the characters a *bold sentence. BMX tells you.

BMX-E003 — unterminated code fence

The commonest way a page becomes one giant code block. Markdown closes the fence for you at end of file and says nothing.

BMX-E004 — unterminated link

see [docs](x

BMX-E004 at 4: unterminated link target

Also fires when a [text] is not followed by (.

BMX-E010 — a tab in significant whitespace

A tab is four columns, or eight, or one, depending on who is looking. A format that promises one reading cannot contain a character whose width is a matter of opinion.

BMX-E011 — malformed heading

#Heading

BMX-E011 at 0: a heading needs exactly one space after its #

Also: seven or more #, and an empty heading. It is not read as a paragraph beginning with # — that reading is how a typo’d heading silently becomes body text.

BMX-E012 — nesting, which 0.1 does not have

- one
  - nested

BMX-E012 at 6: 0.1 has no nesting; this line is indented

Refused rather than guessed at. The tree already nests; only the parser declines, and a real document that needs it is what would earn it a version.

BMX-E020 — unterminated code span

An unclosed `.

BMX-E021 — invalid escape

a \q b

BMX-E021 at 2: only ` * [ { and \ may be escaped

A backslash that sometimes escapes and sometimes is a backslash is how every markdown dialect ends up with a different answer.

BMX-E022 — empty slot expression

{{ }} — nothing to evaluate.

Render-time errors

These are the host’s rather than the format’s, so the codes are Burxt’s. Another implementation may name them differently; it must still refuse.

BMX-R001 — a link target with a disallowed scheme

BMX-R001: refused a link target whose scheme is not http, https or mailto: javascript:steal

Not a character-escaping problem — the danger is the scheme, and escaping every byte of javascript: changes nothing. An implementation written in an afternoon will not think of this, which is why the spec requires it rather than suggesting it.

BMX-R002 — a slot with no binding

BMX-R002: no binding for slot `order.totl` at 10

An error, never an empty string. Every template language in wide use renders the empty string here, and that is how a page ships with a missing total that nobody sees.

At level 2 you never meet this one: the same typo is a compile error naming the field and listing what the type actually has.

BMX-G001 — a dangerous link target, at build time

The generator refuses it before a page exists. A document’s targets are static text, so this never needs to reach a render.

Reading an offset

The offset is a byte index into the document, and for a slot it points at the first byte of the expression — not at the {{. For Hello {{ user.name }}. it is 9, the u.

That is so a host can underline the text it is complaining about. It is the only reason the field exists, and getting it wrong is caught by the conformance suite: 023-slot-offset-survives-a-stripped-line exists because an early implementation reported an offset three bytes early inside a multi-line paragraph, off by the trailing spaces stripped from an earlier line.