What are invalid characters in XML

Eef_30786 0
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I am working with some XML that holds strings like:

<node>This is a string</node>

Some of the strings that I am passing to the nodes will have characters like &, #, $, etc.:

<node>This is a string & so is this</node>

This is not valid due to &.

I cannot wrap these strings in CDATA as they need to be as they are. I tried looking for a list of characters that cannot be put in XML nodes without being in a CDATA.

Can someone point me in the direction of one or provide me with a list of illegal characters?

xml
15 Answers

The only illegal characters are &, < and > (as well as " or ' in attributes, depending on which character is used to delimit the attribute value: attr="must use &quot; here, ' is allowed" and attr='must use &apos; here, " is allowed').

They're escaped using XML entities, in this case you want &amp; for &.

Really, though, you should use a tool or library that writes XML for you and abstracts this kind of thing away for you so you don't have to worry about it.

Welbog_524430
altCognito_389710
user_8716810

In summary, valid characters in the text are:

  • tab, line-feed and carriage-return.
  • all non-control characters are valid except & and <.
  • > is not valid if following ]].

Sections 2.2 and 2.4 of the XML specification provide the answer in detail:

Characters

Legal characters are tab, carriage return, line feed, and the legal characters of Unicode and ISO/IEC 10646

Character data

The ampersand character (&) and the left angle bracket (<) must not appear in their literal form, except when used as markup delimiters, or within a comment, a processing instruction, or a CDATA section. If they are needed elsewhere, they must be escaped using either numeric character references or the strings " & " and " < " respectively. The right angle bracket (>) may be represented using the string " > ", and must, for compatibility, be escaped using either " > " or a character reference when it appears in the string " ]]> " in content, when that string is not marking the end of a CDATA section.

user_38007820
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