I still don't understand, why in xsl simple programming code

> ( like for loops , not on the xml, but just like i=0 to 10)
>  is not included.

Not yet mentioned: the original design goal was to
get a language which makes describing transformations
like
  <todo-list>
    <todo>Today...<em>urgent</em>...</todo>
  </todo-list>
into
  <list-block>
    <list-item>
      <list-item-label>*</list-item-label>
      <list-item-body>Today...<inline font-weight="bold>
        urgend</inline>...
      </list-item-body>
    </list-item>
  </list-block>
easy and execution robust with respect to small
changes in the source XML. If general computation
had been the focus, the language would not have been
named XSL but XPL.

This is actually a serious omission. After all, there
is also a format-number.