TypeScript Language Specification v1.5

An ExternalImportDeclaration in an AmbientExternalModuleDeclaration may reference other external
modules only through top-level external module names. Relative external module names are not
permitted.
If an ambient external module declaration includes an export assignment, it is an error for any of the
declarations within the module to specify an export modifier. If an ambient external module declaration
contains no export assignment, entities declared in the module are exported regardless of whether their
declarations include the optional export modifier.
Ambient external modules are "open-ended" and ambient external module declarations with the same
string literal name contribute to a single external module. For example, the following two declarations of
an external module 'io' might be located in separate source files.
declare module "io" {
export function readFile(filename: string): string;
}
declare module "io" {
export function writeFile(filename: string, data: string): void;
}
This has the same effect as a single combined declaration:
declare module "io" {
export function readFile(filename: string): string;
export function writeFile(filename: string, data: string): void;
}
154