Exceptions after changing to developer mode

Question

After I changed to developer mode, I can't view the main page, and get the following exception (Magento 2.1.2)

Invalid XML in file x.com/app/code/Ves/ImageSlider/etc/widget.xml:
Element 'description': This element is not expected. Expected is ( value ).

The issue is labelled to be at this area of the xml file

<parameter name="autoplay_timeout" xsi:type="text" visible="true">
    <label translate="true">Autoplay Timeout</label>
    <depends><parameter name="autoplay" value="1" /></depends>
    <description translate="true"><![CDATA[Default: 3000]]></description>
    <value>3000</value>
</parameter>
<parameter name="autoplay_speed" xsi:type="text" visible="true">
    <label translate="true">Autoplay Speed</label>
    <depends><parameter name="autoplay" value="1" /></depends>
    <description translate="true"><![CDATA[Default: 800]]></description>
    <value>800</value>
</parameter>

Answer 1

move the description tag above the depends tag.
In the XSD schema Magento/Widget/etc/widget.xsd the parameter type is defined as this

 <xs:complexType name="parameterType" abstract="true">
    <xs:annotation>
        <xs:documentation>
            Abstract type which is parent of all parameters. Contains attributes
            and elements common across all parameter types.
        </xs:documentation>
    </xs:annotation>
    <xs:sequence>
        <xs:element name="label" type="translatableType" minOccurs="0" maxOccurs="1" />
        <xs:element name="description" type="translatableType" minOccurs="0" maxOccurs="1" />
        <xs:element name="depends" type="dependsType" minOccurs="0" maxOccurs="1" />
    </xs:sequence>
    <xs:attribute name="name" type="xs:NMTOKEN" use="required" />
    <xs:attribute name="visible" type="xs:boolean" />
    <xs:attribute name="sort_order" type="xs:int" />
    <xs:attribute name="required" type="xs:string" />
</xs:complexType>

focus on this part

    <xs:sequence>
        <xs:element name="label" type="translatableType" minOccurs="0" maxOccurs="1" />
        <xs:element name="description" type="translatableType" minOccurs="0" maxOccurs="1" />
        <xs:element name="depends" type="dependsType" minOccurs="0" maxOccurs="1" />
     </xs:sequence>

This means that the element parameter supports the child elements listed in the sequence tag in this order. label, description, depends.

Side node: Ignore the fact that you don't see the value tag in here. This is added later in the same file depending on the value of the parameter type