// simple interface
interface TallPerson {
    firstName: string;
	lastName: string;
	middleInit?: string;    // optional property
	readonly x: number;     // only be modifiable when an object is first created
	(source: string, subString: string): boolean;   // a function type - only defines params and return types
	[index: number]: string;    // Indexable types to describe array. index sig describes types i.e.:["Bob", "Fred"]
	[propName: string]: any;    // index signature - object can have any number of additional props and still be valid
}