whitespace at the beginning and the end of element content

[Wolfgang Jeltsch <wolfgang@jeltsch.net>]

Hello,

in which element's content is whitespace at the beginning or the end 
significant?  For example, if I write

    <wordasword> word </wordasword>

and convert to PDF, I assume that there will be a space before and after 
"word" in the output.  But what if I write

    <para>
      This is a paragraph.
    </para>?

Will there be unwanted space at the beginning and the end of the paragraph or 
are these spaces and linebreaks ignored?

How can I find out for which elements whitespace at the beginning and end of 
element content is significant and for which it is not?

Best whishes,
Wolfgang