What is the meaning in of this PHP line '<<<XML  XML' i can;t seem to parse this right

I have this php line in magento rest api for inserting a product image. It works but I need to know whats happening because it causes error sometimes parsing. thanks

$xmlstr = <<<XML
<magento_api>
<file_mime_type>image/jpeg</file_mime_type
<file_content>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
</file_content>
<file_name>test</file_name>
</magento_api>
XML;

Solution

It's heredoc syntax - the lines between <<<XML and XML; are treated as a string value.

It can be useful if you want to ignore quotation issues (mixed ' and ") and is often picked up by syntax highlighting (TXT, SQL, HTML are also common identifiers.)

Parsing errors are often caused by ignoring the following warning:

It is very important to note that the line with the closing identifier must contain no other characters, except a semicolon (;). That means especially that the identifier may not be indented, and there may not be any spaces or tabs before or after the semicolon. It's also important to realize that the first character before the closing identifier must be a newline as defined by the local operating system. This is \n on UNIX systems, including Mac OS X. The closing delimiter must also be followed by a newline.