有什么作用<! ... !>在 XML 中是什么意思？

Question

What does <! ... !> <! ... !> mean in XML?

This <? ... ?> <? ... ?> specifies a processing instruction according to this , but I found no information regarding the first one.

Answer 1

<! ... !> <! ... !> is not an XML construct due to the ending !> .

However, the following XML constructs do begin with <! :

• <!-- begins a comment , which ends with -->

• <![CDATA[ begins a CDATA section , which ends with ]]>

• <![INCLUDE[ and <![IGNORE[ begin conditional sections , which end with ]]> .

• <!DOCTYPE begins a document type declaration .

• <!ELEMENT begins an element type declaration .

• <!ATTLIST begins an attribute list declaration .

• <!ENTITY begins an entity declaration .

• <!NOTATION begins a notation declaration .

The ending of each of the above constructions is > unless otherwise mentioned.