BreadcrumbList: BreadcrumbList
In cboettig/schemar: Create Structured Data Using the Schema.org Vocabulary

Description Usage Arguments Value

A BreadcrumbList is an ItemList consisting of a chain of linked Web pages, typically described using at least their URL and their name, and typically ending with the current page.The [[position]] property is used to reconstruct the order of the items in a BreadcrumbList The convention is that a breadcrumb list has an [[itemListOrder]] of [[ItemListOrderAscending]] (lower values listed first), and that the first items in this list correspond to the "top" or beginning of the breadcrumb trail, e.g. with a site or section homepage. The specific values of 'position' are not assigned meaning for a BreadcrumbList, but they should be integers, e.g. beginning with '1' for the first item in the list.

BreadcrumbList(id = NULL, numberOfItems = NULL, itemListOrder = NULL,
  itemListElement = NULL, url = NULL, sameAs = NULL,
  potentialAction = NULL, name = NULL, mainEntityOfPage = NULL,
  image = NULL, identifier = NULL, disambiguatingDescription = NULL,
  description = NULL, alternateName = NULL, additionalType = NULL)

`id`	identifier for the object (URI)
`numberOfItems`	(Integer type.) The number of items in an ItemList. Note that some descriptions might not fully describe all items in a list (e.g., multi-page pagination); in such cases, the numberOfItems would be for the entire list.
`itemListOrder`	(Text or ItemListOrderType type.) Type of ordering (e.g. Ascending, Descending, Unordered).
`itemListElement`	(Thing or Text or ListItem type.) For itemListElement values, you can use simple strings (e.g. "Peter", "Paul", "Mary"), existing entities, or use ListItem.Text values are best if the elements in the list are plain strings. Existing entities are best for a simple, unordered list of existing things in your data. ListItem is used with ordered lists when you want to provide additional context about the element in that list or when the same item might be in different places in different lists.Note: The order of elements in your mark-up is not sufficient for indicating the order or elements. Use ListItem with a 'position' property in such cases.
`url`	(URL type.) URL of the item.
`sameAs`	(URL type.) URL of a reference Web page that unambiguously indicates the item's identity. E.g. the URL of the item's Wikipedia page, Wikidata entry, or official website.
`potentialAction`	(Action type.) Indicates a potential Action, which describes an idealized action in which this thing would play an 'object' role.
`name`	(Text type.) The name of the item.
`mainEntityOfPage`	(URL or CreativeWork type.) Indicates a page (or other CreativeWork) for which this thing is the main entity being described. See [background notes](/docs/datamodel.html#mainEntityBackground) for details.
`image`	(URL or ImageObject type.) An image of the item. This can be a [[URL]] or a fully described [[ImageObject]].
`identifier`	(URL or Text or PropertyValue type.) The identifier property represents any kind of identifier for any kind of [[Thing]], such as ISBNs, GTIN codes, UUIDs etc. Schema.org provides dedicated properties for representing many of these, either as textual strings or as URL (URI) links. See [background notes](/docs/datamodel.html#identifierBg) for more details.
`disambiguatingDescription`	(Text type.) A sub property of description. A short description of the item used to disambiguate from other, similar items. Information from other properties (in particular, name) may be necessary for the description to be useful for disambiguation.
`description`	(Text type.) A description of the item.
`alternateName`	(Text type.) An alias for the item.
`additionalType`	(URL type.) An additional type for the item, typically used for adding more specific types from external vocabularies in microdata syntax. This is a relationship between something and a class that the thing is in. In RDFa syntax, it is better to use the native RDFa syntax - the 'typeof' attribute - for multiple types. Schema.org tools may have only weaker understanding of extra types, in particular those defined externally.