`swift-markdown` doesn't detect Strong correctly in a specific case

[fumo1222]

swift-markdown doesn't detect Strong in

**b`h`** + letters or numbers

Examples:
**b`h`**abc
**b`h`**3k

Strong is correctly detected when the strings right after the markdown start with a sign, such as:

Examples:
**b`h`**=ab
**b`h`**/

or there is a space, such as:

Example:
**b`h`** a

I think swift-markdown should detect Strong in the first case as well.

Steps to reproduce

let markdown = "**b`h`**a"
let document = Document(parsing: markdown)
print("\(document.debugDescription())")

Expected output:

Document
└─ Paragraph
   ├─ Strong
   │  ├─ Text "b"
   │  └─ InlineCode `h`
   └─ Text "a"

Actual Output:

** isn't detected as Bold but as plain text.

Document
└─ Paragraph
   ├─ Text "**b"
   ├─ InlineCode `h`
   └─ Text "**a"

Similar situations where it works as expected

let markdown = "**b`h`** c"

Document
└─ Paragraph
   ├─ Strong
   │  ├─ Text "b"
   │  └─ InlineCode `h`
   └─ Text " c"

let markdown = "**b`h`**="

Document
└─ Paragraph
   ├─ Strong
   │  ├─ Text "b"
   │  └─ InlineCode `h`
   └─ Text "="

let markdown = "**`b`h**a"

Document
└─ Paragraph
   ├─ Strong
   │  ├─ InlineCode `b`
   │  └─ Text "h"
   └─ Text "a"

let markdown = "**b~h~**a"

Document
└─ Paragraph
   ├─ Strong
   │  ├─ Text "b"
   │  └─ Strikethrough
   │     └─ Text "h"
   └─ Text "a"

let markdown = "**b*h***a"

Document
└─ Paragraph
   ├─ Strong
   │  ├─ Text "b"
   │  └─ Emphasis
   │     └─ Text "h"
   └─ Text "a"

Environment

• swift-markdown version: 0.4.0
• Xcode version: 15.4 (15F31d)
• macOS version: 14.3.1（23D60）

[QuietMisdreavus]

This is expected behavior. Emphasis delimiters cannot close emphasis if they are between punctuation and alphanumeric characters. This is part of the upstream GitHub-Flavored Markdown specification as well as the spec and implementation for its upstream CommonMark.