:sig
String markdown_to_html(String src)
String markdown_to_html(String src, DTree options)

:params
src : markdown source text
options : optional markdown options tree
return value : rendered HTML string

:desc
Renders Markdown source into HTML and returns the generated markup as a `String`.

`markdown_to_html()` does not write to the output stream directly. This keeps it aligned with the UCE naming convention where `render_*` names are reserved for direct-output helpers.

Because the return value is HTML markup, embed it with `<?: markdown_to_html(...) ?>`, `print(markdown_to_html(...))`, or pass it through a component.

By default the function aims at a practical GitHub-flavored Markdown target, including tables, task lists, fenced code blocks, autolinks, and strikethrough.

:Example
`DTree options;`
`options["components"][":::warning"] = "components/markdown/warning";`
`options["components"]["node.code_block"] = "components/markdown/code_block";`
`String html = markdown_to_html(file_get_contents("guide.md"), options);`
`print(html);`

:SupportedSyntax
- headings with `#` or setext underlines
- paragraphs
- ordered and unordered lists
- task lists
- blockquotes
- fenced code blocks
- horizontal rules
- tables
- inline emphasis, strong, strikethrough, code spans
- links, images, and bare `http://` / `https://` URLs
- `:::name ... :::` directive blocks

:Options
`options["gfm"]`
Defaults to true.
Turns on GitHub-style extras such as tables, task lists, autolinks, and strikethrough.

`options["allow_html"]`
Defaults to false.
When true, raw HTML blocks and inline tags may pass through as `raw_html` nodes instead of being escaped as plain text.

`options["components"]`
Declares renderer extension points using normal UCE components.

Exact directive hooks:
`options["components"][":::warning"] = "components/markdown/warning"`
This hook is selected for `:::warning ... :::` blocks.

Generic node hooks:
`options["components"]["node.code_block"] = "components/markdown/code_block"`
`options["components"]["node.table"] = "components/markdown/table"`
`options["components"]["node.link"] = "components/markdown/link"`
`options["components"]["node.directive"] = "components/markdown/directive"`

If both an exact directive hook and a generic `node.directive` hook exist, the exact directive hook wins.

:ComponentProps
When a markdown hook component is called, its props arrive in `context.call`.

Useful fields include:
`context.call["hook"]` : matched hook key such as `:::warning` or `node.code_block`
`context.call["target"]` : resolved component target name
`context.call["default_html"]` : renderer output without the hook
`context.call["children_html"]` : already-rendered child HTML
`context.call["node"]` : full AST node
`context.call["type"]` : node type
`context.call["name"]` : directive name when applicable
`context.call["argument"]` : directive remainder after the name
`context.call["text"]` : source text for nodes such as `code_block`
`context.call["lang"]` : fenced code language
`context.call["href"]` / `context.call["src"]` / `context.call["title"]`
`context.call["options"]` : full markdown options tree

This lets a component either replace the HTML completely or wrap `default_html` / `children_html`.

:DirectiveSchema
Directive blocks use this form:
`:::warning title="Heads up"`
`Body markdown here`
`:::`

The parser stores:
`node["name"] = "warning"`
`node["argument"] = ...` for bare trailing text
`node["attrs"] = ...` for parsed `key=value` pairs such as `title="Heads up"`

This makes directive components a good fit for alerts, callouts, cards, embeds, and any richer page-level markdown extension.

:see
markdown_to_ast
component
render_component
json_decode
String