Troubleshooting Guide: How to Resolve the Processing Instruction Target Matching '[xx][mm][ll]' Error

In this troubleshooting guide, we will walk you through the steps to resolve the Processing Instruction Target Matching '[xx][mm][ll]' error. This error is commonly encountered when working with XML documents, and it can be caused by various issues, such as incorrect syntax, encoding issues, or problems with the XML parser.

Table of Contents

  1. Understanding the Error
  2. Step-by-Step Solution
  3. FAQs
  4. Related Links

Understanding the Error

The Processing Instruction Target Matching '[xx][mm][ll]' error occurs when the XML parser encounters a processing instruction target that matches the pattern xml in any combination of uppercase or lowercase letters. This is reserved for XML standard processing instructions and cannot be used for custom processing instructions.

For example, the following XML document will trigger this error:

<?xml version="1.0" encoding="UTF-8"?>
  <?xml-custom Processing Instruction?>

Step-by-Step Solution

To resolve the Processing Instruction Target Matching '[xx][mm][ll]' error, follow the steps below:

Identify the problematic processing instruction: Locate the processing instruction in your XML document that is causing the error. It will have a target matching the pattern xml in any combination of uppercase or lowercase letters.

Update the processing instruction target: Change the processing instruction target to something other than xml in any case. Ensure that the updated target is compliant with the XML specification.

For example, you can change the processing instruction in the previous example to:

<?custom-xml Processing Instruction?>

Validate your XML document: After updating the processing instruction target, validate your XML document to ensure that it is well-formed and free of errors. You can use online tools like XML Validator or W3C's XML Validator to validate your document.

  1. Fix any additional errors: If the validator reports any other errors or issues, fix them and re-validate your XML document.

Following the above steps should resolve the Processing Instruction Target Matching '[xx][mm][ll]' error in your XML document.


Why is the processing instruction target 'xml' reserved?

The processing instruction target 'xml' is reserved because it is used for standard XML processing instructions, such as defining the XML version and encoding. Using it for custom processing instructions can cause conflicts and confusion for XML parsers.

Can I use a different case for the 'xml' target?

No, the 'xml' target is case-insensitive and cannot be used in any combination of uppercase or lowercase letters for custom processing instructions.

What characters are allowed in a processing instruction target?

According to the XML specification, a processing instruction target must start with a letter or an underscore and can be followed by any combination of letters, digits, hyphens, underscores, and periods.

How can I define custom processing instructions in my XML document?

You can define custom processing instructions by using a target that does not match the reserved 'xml' pattern in any case. For example:

<?custom-processing-instruction data?>

Can processing instructions contain attributes like XML elements?

No, processing instructions do not support attributes like XML elements. Any data included in the processing instruction should be treated as a single string.

  1. W3C XML Specification: Processing Instructions
  2. XML Validator
  3. W3C's XML Validator
  4. Introduction to XML Processing Instructions

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