<sch:rule context="mei:*[@confidence]">
                              
                              <sch:assert test="@min and @max">The attributes @min and @max are required when
                                 @confidence is present.</sch:assert>
                              </sch:rule>
                     <classSpec ident="att.ranging" module="MEI.shared" type="atts">
                        
                        <desc>Groups attributes that describe a numerical range.</desc>
                        
                        <attList org="group">
                           
                           <attDef ident="atleast" usage="opt">
                              
                              <desc>Gives a minimum estimated value for an approximate measurement.</desc>
                              
                              <datatype maxOccurs="1" minOccurs="1">
                                 
                                 <rng:data type="decimal"/>
                                 </datatype>
                              </attDef>
                           
                           <attDef ident="atmost" usage="opt">
                              
                              <desc>Gives a maximum estimated value for an approximate measurement.</desc>
                              
                              <datatype maxOccurs="1" minOccurs="1">
                                 
                                 <rng:data type="decimal"/>
                                 </datatype>
                              </attDef>
                           
                           <attDef ident="min" usage="opt">
                              
                              <desc>Where the measurement summarizes more than one observation or a range of values,
                                 supplies the minimum value observed.</desc>
                              
                              <datatype maxOccurs="1" minOccurs="1">
                                 
                                 <rng:data type="decimal"/>
                                 </datatype>
                              </attDef>
                           
                           <attDef ident="max" usage="opt">
                              
                              <desc>Where the measurement summarizes more than one observation or a range of values,
                                 supplies the maximum value observed.</desc>
                              
                              <datatype maxOccurs="1" minOccurs="1">
                                 
                                 <rng:data type="decimal"/>
                                 </datatype>
                              </attDef>
                           
                           <attDef ident="confidence" usage="opt">
                              
                              <desc>Specifies the degree of statistical confidence (between zero and one) that a value
                                 falls within the range specified by min and max, or the proportion of observed values
                                 that
                                 fall within that range.</desc>
                              
                              
                              
                              <constraintSpec ident="check_confidence" scheme="isoschematron">
                                 
                                 <constraint>
                                    
                                    <sch:rule context="mei:*[@confidence]">
                                       
                                       <sch:assert test="@min and @max">The attributes @min and @max are required when
                                          @confidence is present.</sch:assert>
                                       </sch:rule>
                                    </constraint>
                                 </constraintSpec>
                              </attDef>
                           </attList>
                        </classSpec>