On all of my Visualforce Pages that involve user input and DML actions I include the handy
<apex:pageMessages/> tag. This is great when I'm creating my own custom error messages, and in some instances if there is a validation rule failure it has it's own page message automatically created. However, this seems to occur rather erratically. Are there any rules out there for when a validation rule failure will automatically generate it's own page message and when I need to make sure to create them manually?
Please note this is not a question about specific piece of code that isn't displaying a message, but rather a question about when Salesforce automatically creates a page message for you that will be shown in the
<apex:pageMessages/> tag and when Salesforce will NOT automatically create a page message for you that will be shown.
For the purpose of this question please assume that I'm either doing a full page refresh or am rerendering the page messages component.