# `Expresso.Element.Focus`
[🔗](https://github.com/rellen/expresso/blob/main/lib/expresso/element/focus.ex#L1)

A group of the `highlight` option of a chart

`Expresso.Element.Chart.check/1` makes one group for each item of the
option, with the specification `:next`. The groups go into the `focus`
field of the chart, and not into its series. `Expresso.Overlay.Expand`
gives each group one step from the counter of the slide, and
`Expresso.Element.Chart.rules/1` dims each part of the chart that is not in
the group at that step. A group is not an entity of the DSL.

A group holds series or categories, and not both:

- The `series` field holds the color number of each series of the group,
  from 1. The color number is also the value of the `data-series`
  attribute of the series.
- The `keys` field holds the key of each category of the group, such as
  `"c2"` for the second category, or `"p3"` for the part or the group with
  the id 3 in a treemap or a sunburst. Each mark of a category has its key
  in its `data-keys` attribute. A chart of flows takes nodes in place of
  categories, such as `"n2"` for the second node.

# `t`

```elixir
@type t() :: %Expresso.Element.Focus{
  at: term(),
  easing: term(),
  effect: term(),
  el: term(),
  keys: term(),
  morph: term(),
  on: term(),
  series: term(),
  signature: term(),
  speed: term(),
  steps: term()
}
```

The struct of a group of the highlight option

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*Consult [api-reference.md](api-reference.md) for complete listing*