:sig
String yaml_encode(DTree t)

:params
t : tree to serialize as YAML
return value : YAML string

:see
>markup
yaml_decode
json_encode
xml_encode
0_DTree

:content
Serializes a `DTree` into a compact YAML string for configuration files.

`yaml_encode()` focuses on the ordinary data shapes UCE apps use for config: nested maps, lists, strings, booleans, and numeric `f64` values. It does not emit YAML tags, anchors, aliases, or custom schema features.

Try the live example in the [YAML demo](../demo/yaml.uce).

Example:

```uce
DTree cfg;
cfg["app"]["name"] = "UCE Starter";
cfg["app"]["debug"].set_bool(true);
cfg["app"]["port"] = (f64)8080;

DTree path;
path = "site";
cfg["app"]["paths"].push(path);
path = "cache";
cfg["app"]["paths"].push(path);

String yaml = yaml_encode(cfg);
```

Typical result:

```yaml
app:
  debug: true
  name: UCE Starter
  paths:
    - site
    - cache
  port: 8080
```

Notes:

- Map keys are emitted in `DTree` map iteration order.
- Strings are left plain when safe and quoted when needed.
- Multiline strings are emitted as literal block scalars with `|`.
- Empty strings are emitted as `""` so they are not confused with YAML null.
- Decoded numeric-looking config values are strings unless the original `DTree` value was explicitly numeric.