Custom Labels and Error Messages

Question

The Adding and Customizing Input Field Labels documentation says:

When set, the label attribute will be used for component-level error messages, for example, when a field is required or must be unique. Custom labels won't be used in custom error messages, and the default object field label will be used instead. If you set a label attribute to an empty string, the default object field label will be used in all error messages.

I'm not able to understand above statement; we can access custom labels in the apex with using $Label directly.

Answer 1

It simply means:

1. When you have a label attribute, the component level error message would show error in context label passed in attribute.
2. When your have a empty label attribute or does not have a label attribute at all, it would not show any message with the default field's label.

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Difficult to understand; maybe it would be clear when you try the example.

Output on click of save when email is empty (code at the end)-

Note: Error message for second and third sections/input are same (as apex:pageMessage doesn’t show duplicate message), default message with field's label; only difference is in #3 we have empty label hence it doesn't show a field label because its expecting us to add.

Code for illustration:

<apex:page standardController="Contact">
    <apex:form id="form">
        <apex:pageMessages></apex:pageMessages>
        <apex:pageBlock title="Quick Edit: {!Contact.Name}">
            <apex:pageBlockSection title="1. Dynamic Label" columns="1">
                <apex:inputText value="{!Contact.Email}" 
                    label="{!Contact.FirstName + '’s Email'}" required="true"/>
            </apex:pageBlockSection>
            <apex:pageBlockSection title="2. No label" columns="1">
                <apex:inputText value="{!Contact.Email}" required="true"/>
            </apex:pageBlockSection>
            <apex:pageBlockSection title="3. Empty label" columns="1">
                <apex:inputText value="{!Contact.Email}" label="" required="true"/>
            </apex:pageBlockSection>
            <apex:pageBlockSection title="4. From custom Label" columns="1">
                <apex:inputText value="{!Contact.Email}" 
                    label="{!$Label.Label_Contact_Email}" required="true"/>
            </apex:pageBlockSection>
            <apex:pageBlockButtons >
                <apex:commandButton action="{!save}" value="Save" rerender="form"/>
            </apex:pageBlockButtons>
        </apex:pageBlock>
    </apex:form>
</apex:page>