Read and Write the same file

[JonathanB]

Ok, so this is the scenario. I need to create a simple, no-frills XML
editor for non-technical users. It doesn't have to do anything fancy,
what I want is a series of text boxes with the text contents of the
elements pre-printed. Then the users can type their changes into the
text boxes and click submit and it will load the changes in. So here
is the problem, this means I need to open the same file as both read
and write. How do I do this? I'm slowly learning the DOM stuff that I
need to know to do this, but this file thing I haven't been able to
find anywhere.

JonathanB