Function: extra_data

DOC_MSE_VERSION: since 2.2.0

--Usage--
> extra_data("field_name")

Access the value of extra card fields.

Due to lazy initialization of stylesheet specific Extra Card Fields they are not exposed directly from the card using `card.field_name` syntax.
As a workaround this function returns the Value of the specified field name for the active card using an access pattern that supports late resolution of the value for the active stylesheet.

--Parameters--
! Parameter	Type	Description
| @input@	[[type:string]]	Field name, with or without underscores.

--Examples--

>extra card field:
>	...
>	name: my first extra field
>
>extra card field:
>	...
>	name: my second extra field
>	script:
>>		space_to_comma(extra_data("my first extra field")) + "!"
