Writes a portion of a string.

Parameters:

str     A String

off     Offset from which to start writing characters

len     Number of characters to write

Exceptions:

IndexOutOfBoundsException Implementations should throw this exception if off is negative, or len is negative, or off + len is negative or greater than the length of the given string

IOException If an I/O error occurs

@implSpec The implementation in this class throws an IndexOutOfBoundsException for the indicated conditions; overriding methods may choose to do otherwise.

`str`		A String
`off`		Offset from which to start writing characters
`len`		Number of characters to write

`IndexOutOfBoundsException`		Implementations should throw this exception if `off` is negative, or `len` is negative, or `off + len` is negative or greater than the length of the given string
`IOException`		If an I/O error occurs