``` ucm
scratch/main> builtins.mergeio

  Done.

```
Supports fences that are longer than three backticks.

```` unison
doc = {{
  @typecheck ```
  x = 3
  ```
}}

````

``` ucm

  Loading changes detected in scratch.u.

  I found and typechecked these definitions in scratch.u. If you
  do an `add` or `update`, here's how your codebase would
  change:
  
    ⍟ These new definitions are ok to `add`:
    
      doc : Doc2

```
And round-trips properly.

``` ucm
scratch/main> add

  ⍟ I've added these definitions:
  
    doc : Doc2

scratch/main> edit doc

  ☝️
  
  I added 1 definitions to the top of scratch.u
  
  You can edit them there, then run `update` to replace the
  definitions currently in this namespace.

scratch/main> load scratch.u

  Loading changes detected in scratch.u.

  I found and typechecked the definitions in scratch.u. This
  file has been previously added to the codebase.

```
```` unison:added-by-ucm scratch.u
doc : Doc2
doc =
  {{
  @typecheck ```
  x = 3
  ```
  }}
````