Add a warning in the docs about nested <If> blocks

    <p>Only directives that support the <a href="directive-dict.html#Context"

    >directory context</a> can be used within this configuration section.</p>

    <note><title>Not a scripting language</title>

    The name of this directive is very familiar to programmers and admins 

    but it should not be confused with its counterpart in scripting languages.

    For example, the current implementation does not contemplate the possibility

    of having a <directive type="section">If</directive> section inside another

    one (the inner <directive type="section">If</directive> will be ignored).

    </note>

    <note type="warning">

    Certain variables, such as <code>CONTENT_TYPE</code> and other

    response headers, are set after <If> conditions have already

the other hand, <directive type="section" module="core">If</directive> can

be used inside <directive type="section" module="core">Directory</directive>,

<directive type="section" module="core">Location</directive>, and <directive

type="section" module="core">Files</directive> sections. The regex

type="section" module="core">Files</directive> sections (but not inside another

<directive type="section" module="core">If</directive>). The regex

counterparts of the named section behave identically.</p>

<p>Nested sections are merged after non-nested sections of the same type.</p>