I've just begun to read a book on Regular Expressions and in the book
they strongly discourage unintended white spaces.

Here's an excerpt "...Placing unintended white spaces in a regular
expression can radically alter the meaning of the regular expression
and can turn what ought to be matches into nonmatches, and vice versa.
When creating regular expression patterns, you need to be meticulous
about handling whitespace..." taken from Beginning Regular Expressions
by Andrew Watt.

-Regards
Rashmi

As I am an absolute RegEx beginner, please excuse me if this is a
trivial question.

At the moment I am playing with:

 <xsl:analyze-string select="$vstrInput"
regex='([\s]*)(("[^"\\]*((\\.[^"\\]*)*"))|((([-]?[0-9]+)?\.)?[-]?[0-9]+([eE][-+]?[0-9]+)?
))(.*)$' flags="m">

which should match only the first quoted-string or number in the
string-argument.

Is there any way I can split this RegEx on separate lines and/or add
whitespace so that it would be more readable?

--
Cheers,
Dimitre Novatchev