Input bootstrap class used with streams, when encoding is not known (when encoding is specified by application, a
reader is constructed, and then reader-based bootstrapper is used).
This is the threshold used to check what is considered a "small"
write; small writes will be buffered until resulting size will
be above the threshold.
Method called to output typed values (int, long, double, float etc)
that are known not to contain any escapable characters, or anything
else beyond 7-bit ascii range.