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interface Headers {    [Symbol.iterator](): IterableIterator<[string, string]>;    /** Returns an iterator allowing to go through all key/value pairs contained in this object. */    entries(): IterableIterator<[string, string]>;    /** Returns an iterator allowing to go through all keys of the key/value pairs contained in this object. */    keys(): IterableIterator<string>;    /** Returns an iterator allowing to go through all values of the key/value pairs contained in this object. */    values(): IterableIterator<string>;}interface FormData {    [Symbol.iterator](): IterableIterator<[string, FormDataEntryValue]>;    /** Returns an iterator allowing to go through all key/value pairs contained in this object. */    entries(): IterableIterator<[string, FormDataEntryValue]>;    /** Returns an iterator allowing to go through all keys of the key/value pairs contained in this object. */    keys(): IterableIterator<string>;    /** Returns an iterator allowing to go through all values of the key/value pairs contained in this object. */    values(): IterableIterator<FormDataEntryValue>;}