Use Enclose documentation as an excuse to talk about unit arrays

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 <h2 id="units">Units</h2>
-<p>A unit is an atom, or an array with no axes—rank 0. Since it doesn't have any axes, its shape should have no elements. It should be the empty list <code><span class='Bracket'>⟨⟩</span></code> (with a fill of <code><span class='Number'>0</span></code>, like all shapes). As there's no first element in the shape, it's not obvious what the length should be, and a stricter language would just give an error. However, there are some good reasons to use a length of <code><span class='Number'>1</span></code>. First, the total number of elements is 1, meaning that if the length divides this number evenly (as it does for non-unit arrays) then the only possible natural number it can be is 1. Second, many functions that take a list for a particular argument also accept a unit, and treat it as a length-1 array. For example, <code><span class='Number'>5</span><span class='Function'>⥊</span><span class='Value'>a</span></code> and <code><span class='Bracket'>⟨</span><span class='Number'>5</span><span class='Bracket'>⟩</span><span class='Function'>⥊</span><span class='Value'>a</span></code> are identical. Defining <code><span class='Function'>≠</span><span class='Number'>5</span></code> to be <code><span class='Number'>1</span></code> means that <code><span class='Function'>=</span><span class='Value'>s</span><span class='Function'>⥊</span><span class='Value'>a</span></code> is always <code><span class='Function'>≠</span><span class='Value'>s</span></code>.</p>
+<p>A unit is an atom, or an array with no axes—rank 0. (See <a href="enclose.html">Enclose</a> for more about unit arrays). Since it doesn't have any axes, its shape should have no elements. It should be the empty list <code><span class='Bracket'>⟨⟩</span></code> (with a fill of <code><span class='Number'>0</span></code>, like all shapes). As there's no first element in the shape, it's not obvious what the length should be, and a stricter language would just give an error. However, there are some good reasons to use a length of <code><span class='Number'>1</span></code>. First, the total number of elements is 1, meaning that if the length divides this number evenly (as it does for non-unit arrays) then the only possible natural number it can be is 1. Second, many functions that take a list for a particular argument also accept a unit, and treat it as a length-1 array. For example, <code><span class='Number'>5</span><span class='Function'>⥊</span><span class='Value'>a</span></code> and <code><span class='Bracket'>⟨</span><span class='Number'>5</span><span class='Bracket'>⟩</span><span class='Function'>⥊</span><span class='Value'>a</span></code> are identical. Defining <code><span class='Function'>≠</span><span class='Number'>5</span></code> to be <code><span class='Number'>1</span></code> means that <code><span class='Function'>=</span><span class='Value'>s</span><span class='Function'>⥊</span><span class='Value'>a</span></code> is always <code><span class='Function'>≠</span><span class='Value'>s</span></code>.</p>
 <p>Despite this last point, it's important to remember that a unit isn't the same as a 1-element list. For example, the length-1 string <code><span class='String'>&quot;a&quot;</span></code> doesn't match <code><span class='Function'>&lt;</span><span class='String'>'a'</span></code> but instead <code><span class='Bracket'>⟨</span><span class='String'>'a'</span><span class='Bracket'>⟩</span></code>. And also bear in mind that having an empty <em>shape</em> doesn't make a unit an empty <em>array</em>. That would mean it has no elements, not one!</p>
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