GeoServer SLD style : ordering draw from custom attribute

Question

I want to control the order in which the features are being loaded and drawn on the map with the GeoServer vendor parameter sortBy.

1. I created a layer from an external WFS i'm not owner. So i'can't create a Z attribute in the data source.

2. Then, i created succesfully a custom attribute based on this documentation :

   if_then_else(equalTo(MU_SHORT_FRE,'BR'),1,2)

Resulting WFS attributes view and datatype in QGIS

3.Now, i try to add the (validated parse) sld vendor parameter

<?xml version="1.0" encoding="UTF-8"?>
<StyledLayerDescriptor xmlns="http://www.opengis.net/sld" xmlns:ogc="http://www.opengis.net/ogc" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xlink="http://www.w3.org/1999/xlink" xsi:schemaLocation="http://www.opengis.net/sld http://schemas.opengis.net/sld/1.1.0/StyledLayerDescriptor.xsd" version="1.1.0" xmlns:se="http://www.opengis.net/se">
  <NamedLayer>
    <se:Name>Gemeentegrenzen</se:Name>
    <UserStyle>
      <se:Name>Gemeentegrenzen</se:Name>
      <se:FeatureTypeStyle>
        <se:Rule>
          <se:Name>BR</se:Name>
          <se:Description>
            <se:Title>BR</se:Title>
          </se:Description>
          <ogc:Filter xmlns:ogc="http://www.opengis.net/ogc">
            <ogc:PropertyIsEqualTo>
              <ogc:PropertyName>MU_SHORT_FRE</ogc:PropertyName>
              <ogc:Literal>BR</ogc:Literal>
            </ogc:PropertyIsEqualTo>
          </ogc:Filter>
          <se:PolygonSymbolizer>
            <se:Stroke>
              <se:SvgParameter name="stroke">#ff6283</se:SvgParameter>
              <se:SvgParameter name="stroke-width">3</se:SvgParameter>
              <se:SvgParameter name="stroke-linejoin">bevel</se:SvgParameter>
            </se:Stroke>
          </se:PolygonSymbolizer>
        </se:Rule>
        <se:Rule>
          <se:Name></se:Name>
          <se:ElseFilter xmlns:se="http://www.opengis.net/se"/>
          <se:PolygonSymbolizer>
            <se:Stroke>
              <se:SvgParameter name="stroke">#000000</se:SvgParameter>
              <se:SvgParameter name="stroke-width">1</se:SvgParameter>
              <se:SvgParameter name="stroke-linejoin">bevel</se:SvgParameter>
            </se:Stroke>
          </se:PolygonSymbolizer>
        </se:Rule>
        <se:VendorOption name="sortBy">Z</se:VendorOption>
      </se:FeatureTypeStyle>
    </UserStyle>
  </NamedLayer>
</StyledLayerDescriptor>

I get the following issue as the Z attribute does't exist. (If i write a non existing field name, i get the same issue).

Answer 1

I simply sorted the rendering by using two FeatureTypeStyle blocks as explained in the documentation. The Z parameter vendor is only if you want to use one FeatureTypeStyle.

The impossibility to use custom attributes with Z parameter vendor stays open

<?xml version="1.0" encoding="UTF-8"?>
<StyledLayerDescriptor xmlns="http://www.opengis.net/sld" xmlns:ogc="http://www.opengis.net/ogc" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xlink="http://www.w3.org/1999/xlink" xsi:schemaLocation="http://www.opengis.net/sld http://schemas.opengis.net/sld/1.1.0/StyledLayerDescriptor.xsd" version="1.1.0" xmlns:se="http://www.opengis.net/se">
  <NamedLayer>
    <se:Name>Gemeentegrenzen</se:Name>
    <UserStyle>
      <se:Name>Gemeentegrenzen</se:Name>
      <se:FeatureTypeStyle>
        <se:Rule>
          <se:Name>Else</se:Name>
          <se:Description>
            <se:Title>Others</se:Title>
          </se:Description>
          <se:ElseFilter xmlns:se="http://www.opengis.net/se"/>
          <se:PolygonSymbolizer>
            <se:Stroke>
              <se:SvgParameter name="stroke">#000000</se:SvgParameter>
              <se:SvgParameter name="stroke-width">1</se:SvgParameter>
              <se:SvgParameter name="stroke-linejoin">bevel</se:SvgParameter>
            </se:Stroke>
          </se:PolygonSymbolizer>
        </se:Rule>
      </se:FeatureTypeStyle>
      <se:FeatureTypeStyle>
        <se:Rule>
          <se:Name>BR</se:Name>
          <se:Description>
            <se:Title>Brussels</se:Title>
          </se:Description>
          <ogc:Filter xmlns:ogc="http://www.opengis.net/ogc">
            <ogc:PropertyIsEqualTo>
              <ogc:PropertyName>MU_SHORT_FRE</ogc:PropertyName>
              <ogc:Literal>BR</ogc:Literal>
            </ogc:PropertyIsEqualTo>
          </ogc:Filter>
          <se:PolygonSymbolizer>
            <se:Stroke>
              <se:SvgParameter name="stroke">#ff6283</se:SvgParameter>
              <se:SvgParameter name="stroke-width">3</se:SvgParameter>
              <se:SvgParameter name="stroke-linejoin">bevel</se:SvgParameter>
            </se:Stroke>
          </se:PolygonSymbolizer>
        </se:Rule>
      </se:FeatureTypeStyle>
    </UserStyle>
  </NamedLayer>
</StyledLayerDescriptor>