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Document Syntax

XML declaration Root element Elements Attributes Empty elements Comments CDATA sections Entity references

Names & Text

Case sensitivity Well-formed nesting Quoted attributes Escaping ampersand Escaping less-than Whitespace preservation xml:space Unicode content

Namespaces

Default namespace Prefixed namespace Namespace declaration Qualified element names Qualified attributes Namespace scope Multiple vocabularies Namespace URI identity

DTD Basics

DOCTYPE declaration Element declaration Attribute declaration Internal entity External entity risk ID attribute concept DTD validation concept Mixed content

XML Schema Concepts

Schema namespace Element type Simple type Complex type Sequence Choice Occurrence constraints Attribute requirement

Processing & Integration

XPath selection XSLT transform concept DOM parsing concept SAX streaming concept XML serialization Canonicalization concept XXE prevention Content-Type application/xml

XML / DTD Basics

External entity risk

Learn External entity risk in XML with a dedicated explanation, a concept-specific example, a production caution, and a mastery check.

12 min read • Intermediate

xml-029.xml

xml

<!-- Do not allow untrusted external entity resolution. -->
<!DOCTYPE data [<!ENTITY ext SYSTEM "file:///etc/passwd">]>
<data>&ext;</data>

What to watch

Content source & attribution

Original Syntaxis Content · Original Syntaxis Content

Lesson quizzes

External entity risk Mastery Check →

Internal entity

ID attribute concept