[marc_omorain]

At CircleCI, we have had to handle many strange YAML documents. Two that come to mind:

A recursive document:

    key: &anchor
     - *anchor

The `~` character represents null:

    ~:
     - ~

This parses as a map of {null: [null]}

[Hendrikto]

What were the authors trying to accomplish with these strange documents?

[marc_omorain]

The recursive anchors seemed to be user-error. Either copy+paste bugs, or an anchors places in the wrong position.

The null character would appear when people try to write a string path, and use the the `~` character without quotes.

[tiagod]

Break their parser, probably