Update 1.3 userdocs

public/docs/user/1.3/_sources/signNverify.rst.txt

@@ -273,7 +273,7 @@ As well as the default behaviour, which signs all objects, fine-grained
 control of signing is possible.
 
 If you ``sif list`` a SIF file you will see it is comprised of a number
-of objects. Each object has an ``ID``, and belongs to a ``GROUP``.
+of objects. Each object has an ``ID``, and belongs to a ``GROUP``. Since signatures are *applied* to objects, they have an ``ID`` but not a ``GROUP``.
 
 .. code::
 

public/docs/user/1.3/signNverify.html

@@ -369,7 +369,7 @@ <h3>Advanced Signing - SIF IDs and Groups<a class="headerlink" href="#advanced-s
 <p>As well as the default behaviour, which signs all objects, fine-grained
 control of signing is possible.</p>
 <p>If you <code class="docutils literal notranslate"><span class="pre">sif</span> <span class="pre">list</span></code> a SIF file you will see it is comprised of a number
-of objects. Each object has an <code class="docutils literal notranslate"><span class="pre">ID</span></code>, and belongs to a <code class="docutils literal notranslate"><span class="pre">GROUP</span></code>.</p>
+of objects. Each object has an <code class="docutils literal notranslate"><span class="pre">ID</span></code>, and belongs to a <code class="docutils literal notranslate"><span class="pre">GROUP</span></code>. Since signatures are <em>applied</em> to objects, they have an <code class="docutils literal notranslate"><span class="pre">ID</span></code> but not a <code class="docutils literal notranslate"><span class="pre">GROUP</span></code>.</p>
 <div class="highlight-default notranslate"><div class="highlight"><pre><span></span>$ apptainer sif list my_container.sif
 
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