This rule is triggered when the symbols used in the document for strong do not
match the configured strong style:

```markdown
**Text**
__Text__
```

To fix this issue, use the configured strong style throughout the document:

```markdown
**Text**
**Text**
```

The configured strong style can be a specific symbol to use (`asterisk`,
`underscore`) or can require all strong matches the first strong (`consistent`).

Note: Emphasis within a word is restricted to `asterisk` in order to avoid
unwanted emphasis for words containing internal underscores like__this__one.

Rationale: Consistent formatting makes it easier to understand a document.