# Emphasis before Korean particles

> Why CommonMark parsers leave `**설정(config)**을` unclosed, the rule mdwire reads it with, and what each channel needs on output — written so other parsers can adopt it.

HTML: https://mdwire.minjun.dev/docs/emphasis/

Korean attaches particles (`을`, `는`, `이다`, `로` …) directly to the word before them, with no space. When
the emphasized word ends in punctuation — a parenthesis, quote, backtick, period or `%` — CommonMark will not
close the emphasis:

```text
**설정(config)**을   **"배포 금지"**는   **`git revert`**로   **끝.**이라서   **52%**다
```

Every CommonMark parser (micromark, markdown-it, lezer, GFM itself) leaves these asterisks as text, and when
there are several on one line the pairs cross and the bold lands on the text between them. LLMs write this
shape all the time. This page states the rule mdwire uses to read it and what each channel needs on output,
so another parser can adopt the same behavior.

## Why CommonMark refuses

A closing `**` must be **right-flanking**: not preceded by whitespace, and either not preceded by
punctuation or followed by whitespace or punctuation. In `**설정(config)**을` the closing run is preceded by
`)` (punctuation) and followed by `을` (a letter), so it is not right-flanking and cannot close. The rule
exists for English, where a word after the run means the run belongs to that word. In Korean the word after
it is a particle of the emphasized word.

The mirror case exists for openers — an opening run preceded by a letter and followed by punctuation
(`값**(합계)**`) is not left-flanking — but it is rare in Korean output.

## The reading rule

mdwire reads emphasis with three changes to CommonMark. Punctuation here means ASCII punctuation plus the
CJK punctuation LLMs write (`，。、！？；：·…—～「」『』（）【】《》`). A **word character** is a letter in any
script or an ASCII digit — symbols such as `①` or `🔥` are not.

1. **Close** — a run closes an open emphasis of the same kind whenever the character before the run is not
   whitespace. The flanking test on the closing side is dropped.
2. **Open** — a run opens when the character after it is not whitespace, and either that character is not
   punctuation or the character before the run is not a word character. This is CommonMark's left-flanking
   test, except that `①**"…"**` opens (a leading symbol is not a word character).
3. **First opener loses** — when a same-kind emphasis is already open and the new run is preceded by
   whitespace and can open, the earlier run is the stray one: it does not pair, and the new run opens. Reading it as a close instead inverts the range — that is
   the line-wrap failure in `채널**이다. …⏎**신분 공개**이`.

Two details keep the rule safe on real text:

- `_` after a letter or digit never **opens** (`snake_case`, `2026-04-29_제목` stay text), but it may close
  (`_진료_가`).
- Emphasis still open at the end of the block is closed there and counted as a repair. It never spreads
  across blocks.

The full reader also handles guesses that turn out wrong (`2 ** 3`, glob `*`), masked numbers
(`4***-****`) and code spans; see `crates/mdwire-core/src/inline.rs` and the
[test cases](https://github.com/minjun0219/mdwire/tree/main/corpus/cases) `punct-before-closing-emphasis`,
`emphasis-across-linebreak`, `asterisk-is-a-letter` and `masked-number-asterisks`.

## Writing it back out

Reading the emphasis correctly is half the job: the channel that renders the output may run CommonMark's
rule again. Measured per channel:

| Channel | Renders `**설정(config)**을`? | What to send |
|---|---|---|
| GitHub (GFM) | No — asterisks stay | `<strong>설정(config)</strong>을` — tags ignore flanking. Only for pairs GFM cannot read. |
| Slack `markdown_text` | No — asterisks stay | `**설정(config)` + U+2060 + `**을` — an invisible word joiner before the closing run. It is neither whitespace nor punctuation, so the run becomes right-flanking. A joiner **after** the run does not help. |
| Notion | Yes | As is. `<strong>` would show as text. |
| Telegram HTML · browser HTML | — | Tags, so the question does not arise. |

Use U+2060 rather than U+200B: both render, but U+200B is a line-break opportunity and U+2060 is not. For an
opener that cannot open, the joiner goes right after the opening run. Measured on 2026-09-30 (GitHub,
`POST /markdown`) and 2026-10-01 (Slack, `chat.postMessage`; Notion, through its API).

To decide when a pair needs this, check both sides with CommonMark's flanking test against the original
neighbors: the character before the opening run and after the closing run. Only pairs that fail get
rewritten; everything else stays as written.