[xml] convert string to encoded string

[Thomas Porschberg <thomas porschberg osp-dd de>]

I want to convert a simple string in
a ISO-8859-1 encoded string with function 
"xmlEncodeEntitiesReentrant"

I tried:
char* mystr;
mystr = (char*)xmlEncodeEntitiesReentrant(NULL, (xmlChar*) "bla & bla");

This worked fine:
I get "bla & bla".

But if I have umlaut like ä or ö I'am not satisfied.
E.g. for "blä & blä" I get:

bl䠦 bl䀀

My first question is: What does this mean?
My second question is: How can I change the code so,
that I will get a ISO-8859-1 encoded string ?
For the example I want:
blä & blä

thomas