The tags <b:message> used for getting explicit message data which value stored at the server side of Blogger, while <b:param/> is additional parameter belong to <b:message>. Rendered message in HTML is vary based on Blog Language Settings.
The Syntax And Attribute
BLOGGER XML LANGUAGE
<b:message name='data:alias'>
<b:param expr:value='data:[STRING]'/>
<b:param value='STRING'/>
</b:message>- Tags <b:message> name value is an alias of data:.
- Tags <b:message> Only accept data:messages type.
- Tags <b:param/> is singleton.
- Tags <b:param/> can be working only if tag <b:message> have parameter.
- Tags <b:param/> value can be data:[STRING] or String.
Examples and Implementation
DATA MESSAGES THAT HAS NO PARAMETERS.
<b:message name='messages.by'/>
messages.by origin is <data:message.by/>, This type of message has no
parameter, so we can't give any <b:param/>.A MESSAGE WITH A PARAMETER
<b:message name='messages.byAuthor'>
<b:param expr:value='data:post.author.name'/>
</b:message>
<b:param/> take data string <data:post.author.name/> which is
who posted the post. For who set Blog language to English, the result will
be By AuthorName.CUSTOMIZE MESSAGE THAT HAS PARAMETER
<b:message name='messages.byAuthorLink'>
<b:param value='foo'/>
<b:param value='https://example.blogspot.com'/>
</b:message>This type of message has two parameters, we can customize it like above. The first <b:param/> is the name and the second one is the link of the author. The result will be 'By Foo' with given link.