Can't get doc examples for custom transforms to work

Replicating the examples from the documentation, for example:

let res = transform({
  filename: 'test.css',
  minify: true,
  code: Buffer.from(`
    .foo {
      overflow: auto;
    }
  `),
  visitor: {
    Property: {
      overflow(property) {
        return [{
          property: 'custom',
          value: {
            name: '-webkit-overflow-scrolling',
            value: [{
              type: 'token',
              value: {
                type: 'ident',
                value: 'touch'
              }
            }]
          }
        }, property];
      },
    }
  }
});

or

let res = transform({
  minify: true,
  code: Buffer.from(`
    .foo {
      size: 12px;
    }
  `),
  visitor: {
    Property: {
      custom: {
        size(property) {
          // Handle the size property when the value is a length.
          if (property.value[0].type === 'length') {
            let value = {
              type: 'length-percentage',
              value: { type: 'dimension', value: property.value[0].value }
            };

            return [
              { property: 'width', value },
              { property: 'height', value }
            ];
          }
        }
      }
    }
  }
});

none of them is working as expected, no value is being replaced.

Start by reproducing the two documentation examples through the transform API and compare the visitor input and output, focusing on why custom properties are not replaced. Trace the transform entry point into the visitor handling and update the relevant behavior or documentation so both examples produce their described replacements; verify with equivalent transform runs.