TypeScript中<P=any>的含义

我看了看 leaflet.js 在定义文件中,我发现了一件奇怪的事情: Marker<P = any> 我想不出是什么 P = any 用于。我是说为什么不是 P: any ?

类实现:

export class Marker<P = any> extends Layer {
    constructor(latlng: LatLngExpression, options?: MarkerOptions);
    toGeoJSON(): geojson.Feature<geojson.Point, P>;
    getLatLng(): LatLng;
    setLatLng(latlng: LatLngExpression): this;
    setZIndexOffset(offset: number): this;
    setIcon(icon: Icon | DivIcon): this;
    setOpacity(opacity: number): this;
    getElement(): HTMLElement | undefined;

    // Properties
    options: MarkerOptions;
    dragging?: Handler;
    feature?: geojson.Feature<geojson.Point, P>;
}

完整定义文件: https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/leaflet/index.d.ts