Is there a way to escape a CDATA end token in xml?

You have to break your data into pieces to conceal the ]]>.

Here's the whole thing:

<![CDATA[]]]]><![CDATA[>]]>

The first <![CDATA[]]]]> has the ]]. The second <![CDATA[>]]> has the >.

Clearly, this question is purely academic. Fortunately, it has a very definite answer.

You cannot escape a CDATA end sequence. Production rule 20 of the XML specification is quite clear:

[20]    CData      ::=      (Char* - (Char* ']]>' Char*))

EDIT: This product rule literally means "A CData section may contain anything you want BUT the sequence ']]>'. No exception.".

EDIT2: The same section also reads:

Within a CDATA section, only the CDEnd string is recognized as markup, so that left angle brackets and ampersands may occur in their literal form; they need not (and cannot) be escaped using "<" and "&". CDATA sections cannot nest.

In other words, it's not possible to use entity reference, markup or any other form of interpreted syntax. The only parsed text inside a CDATA section is ]]>, and it terminates the section.

Hence, it is not possible to escape ]]> within a CDATA section.

EDIT3: The same section also reads:

2.7 CDATA Sections

[Definition: CDATA sections may occur anywhere character data may occur; they are used to escape blocks of text containing characters which would otherwise be recognized as markup. CDATA sections begin with the string "<![CDATA[" and end with the string "]]>":]

Then there may be a CDATA section anywhere character data may occur, including multiple adjacent CDATA sections inplace of a single CDATA section. That allows it to be possible to split the ]]> token and put the two parts of it in adjacent CDATA sections.

ex:

<![CDATA[Certain tokens like ]]> can be difficult and <invalid>]]> 

should be written as

<![CDATA[Certain tokens like ]]]]><![CDATA[> can be difficult and <valid>]]> 

You do not escape the ]]> but you escape the > after ]] by inserting ]]><![CDATA[ before the >, think of this just like a \ in C/Java/PHP/Perl string but only needed before a > and after a ]].

BTW,

S.Lott's answer is the same as this, just worded differently.