OptionalblendBlend modes are used to blend layers together to create an interesting effect in a layer, or even to produce what seems like a new layer.
OptionalcustomA sequence of custom parameters appended to the URL of all requests related to supporting ArcGIS layer types.
OptionaleffectEffect provides various filter functions to achieve different visual effects similar to how image filters (photo apps) work.
OptionalidA unique identifying string for the layer.
OptionalitemOptional string containing the item ID of the service if it's registered on ArcGIS Online or your organization's portal.
OptionallayerA layerDefinition object defining the attribute schema and drawing information for the layer.
OptionallayersAn array of feature layers, each describing the properties for a subtype in the feature service layer.
String indicating the layer type. Value of this property must be SubtypeGroupLayer.
OptionallistIndicates how the layer should display in the table of contents. The known values are listed below. See support/esri!ListMode.
OptionalmaxA number representing the maximum scale at which the layer will be visible. The number is the scale's denominator; thus, a value of 2400 represents a scale of 1/2,400. A value of 0 indicates that the layer will be visible no matter how far you zoom in.
OptionalminA number representing the minimum scale at which the layer will be visible. The number is the scale's denominator; thus, a value of 2400 represents a scale of 1/2,400.
OptionalopacityThe degree of transparency applied to the layer on the client side, where 0 is full transparency and 1 is no transparency.
OptionalrefreshWhen the refresh interval is set on a layer, the client must refresh that layer only, not the entire web map. The default value is '0', meaning the no refresh. You can enable a refresh interval on the following types of layers: ArcGIS Server web service, hosted feature layer, hosted tile layer, OGC WMS, OGS WMTS, tile layer, GeoRSS, Living Atlas layers, basemaps (including Bing Maps basemaps), CSV from the web with latitude and longitude fields, and KML when added to ArcGIS Online through the My Content page. See https://doc.arcgis.com/en/arcgis-online/create-maps/set-refresh-interval.htm.
OptionalshowIndicates whether to allow map authors the ability to control what layers should be shown in a client's legend.
OptionaltimeIndicates whether to disable time animation if the layer supports it.
OptionaltitleA user-friendly title for the layer that can be used in a table of contents. If this is not included, then a title is derived from the service.
Optionaltype(Deprecated, use layerType instead.) If the layer is referenced through a URL, but is not an ArcGIS web service, then this parameter can be supplied to denote the layer type.
OptionalurlThe URL to the layer. If the layer is not from a web service but rather a feature collection, then the url property is omitted.
OptionalvisibilityDetermines whether the layer is initially visible in the web map.
OptionalvisibilityRepresents time extent that will control when a layer should be visible based on webmap's current time. Visibility time extent only affects the layer visibility and will not filter the data.
SubtypeGroupLayer provides the ability to organize several sublayers into one common layer. Suppose there are several FeatureLayers that all represent water features in different dimensions. For example, wells (points), streams (lines), and lakes (polygons). The SubtypeGroupLayer provides the functionality to treat them as one layer called Water Features even though they are stored as separate feature layers.
See https://developers.arcgis.com/web-map-specification/objects/subtypeGroupLayer/.