For certain use cases, this provides a performance improvement,
probably due better cache locality. However, it comes with the cost of
additional memory consumption.
This was initially suggested by Boris Grozev, who also reported a
significant performance problem of
XmlStringBuilder/LazyStringBuilder. However, the main cause of the
performance probelm was the missing caching of LazyStringBuilder. The
length of the lazy string is now cached by LazyStringBuidler since
70e48300a6 ("[core] Cache length in LazyStringBuilder"), which
accounts for large performance improvement. A significantly smaller
improvement is achieved by this commit and setting
XmlStringBuilder.FLAT_APPEND to 'true'.
Suggested-by: Boris Grozev <boris@jitsi.org>