The <interleave> problem

When you begin using Relax NG to describe mixed content, you can come up with this error in your grammar:

<interleave> cannot contain <text/> in more than one branch

Here is what causes this error. Consider a simple weather report that consists of mixed text, with one or more places, low temperatures, and high temperatures.

<report>
Here's your weather report.  The temperatures
for <place>San Jose</place> will be from <low>75</low> to
<high>80</high>. <place>San Francisco</place> will have
temperatures ranging from <low>55</low> to <high>60</high>.
</report>

Here is a correct Relax NG grammar:

<element name="report">
<interleave>
    <text/>
    <oneOrMore>
        <element name="place"> <text/> </element>
        <element name="low"> <data type="integer"/> </element>
        <element name="high"> <data type="integer"/> </element>
    </oneOrMore>
</interleave>
</element>

However, you might think: “There’s text between the <place>, <low> and <high>. So shouln’t I write my grammar this way:” (lines are numbered for reference; line 5 is the one you added):

 1 <element name="report">
 2  <interleave>
 3      <text/>
 4      <oneOrMore>
 5          <text/>
 6          <element name="place"><text/></element>
 7          <element name="low"> <data type="integer"/> </element>
 8          <element name="high"> <data type="integer"/> </element>
 9      </oneOrMore>
10  </interleave>
11  </element>

No, you can’t. That will generate the error. You can have only one <text/> outside an element between a beginning and ending <interleave>. You already have one on line 3; adding the one on line 5 causes the problem. The <text/> on line 6 is just fine, because it is enclosed in an <element>

By the way: the line number in the error message doesn’t give you a clue as to where the error really occurs; you will have to track it down yourself.