Does anybody have any idea about how to solve it?
writer.writeText(summary, component, null);
so all the tags in messages escaped as you already mentioned.
In that functionality we not differs from original h:message(s) components.
If the styling for whole message will helps - you could use component styleClasses.
If not helps and you need to use html tags in messages - put RFC in our jira.
Thanks for your reply!
I've opened a RFC in jira, requesting it as a new feature implementation.