Feature: Support custom starting line number for codeblocks (e.g., start from line 10)

[y122972]

Problem Statement

When sharing code snippets in Markdown (issues, PRs, comments, READMEs, etc.), it is very common to highlight a specific range of lines from a larger file, such as lines 10–20.
(I'm working on some agent app that shows lots of diff codes)

Proposed Solution

// ```javascript {linenos=10}
console.log("This is line 10");
console.log("This is line 11");
// ... up to line 20
// ```

Maybe it already supports this feature? But i can not find docs about that

Alternatives Considered

No response

Use Case

Priority

None

Contribution

• I am willing to help implement this feature

Additional Context

No response

[haydenbleasel]

Hey @y122972 interesting idea! I'll look into this, but as a temporary workaround you should be able to do this by targeting [data-streamdown="code-block-body"] > code and setting the counter increment. For example:

<Streamdown className="[&_[data-streamdown="code-block-body"]>code:[counter-increment:line_6]" />`

That should start the code block at line 6.

This of course modifies all code blocks so it only works if there's a single code block 😂

Will look into implementing your suggestion properly.