# 预定义常量

下列常量由此扩展定义，且仅在此扩展编译入 PHP 或在运行时动态载入时可用。

`LIBXML_BIGLINES` (int)
  Allows line numbers greater than 65535 to be reported correctly.

  > 注意:

  > Only available as of PHP 7.0.0 with Libxml >= 2.9.0

`LIBXML_COMPACT` (int)
  Activate small nodes allocation optimization. This may speed up your application without needing to change the code.

  > 注意:

  > Only available in Libxml >= 2.6.21

`LIBXML_DTDATTR` (int)
  Default DTD attributes
  警告

  Enabling loading of DTD attributes will enable fetching of external entities. The `LIBXML_NO_XXE` constant can be used to prevent this (only available in Libxml >= 2.13.0, as of PHP 8.4.0).

`LIBXML_DTDLOAD` (int)
  Load the external subset
  警告

  Enabling loading of external subsets will enable fetching of external entities. The `LIBXML_NO_XXE` constant can be used to prevent this (only available in Libxml >= 2.13.0, as of PHP 8.4.0).

`LIBXML_DTDVALID` (int)
  Validate with the DTD
  警告

  Enabling validating the DTD may facilitate XML External Entity (XXE) attacks. The `LIBXML_NO_XXE` constant can be used to prevent this (only available in Libxml >= 2.13.0, as of PHP 8.4.0).

`LIBXML_HTML_NOIMPLIED` (int)
  Sets HTML_PARSE_NOIMPLIED flag, which turns off the automatic adding of implied html/body... elements.

  > 注意:

  > Only available in Libxml >= 2.7.7 (as of PHP >= 5.4.0)

`LIBXML_HTML_NODEFDTD` (int)
  Sets HTML_PARSE_NODEFDTD flag, which prevents a default doctype being added when one is not found.

  > 注意:

  > Only available in Libxml >= 2.7.8 (as of PHP >= 5.4.0)

`LIBXML_LOADED_VERSION` (string)
  Version of libxml's core parser module.
`LIBXML_NOBLANKS` (int)
  Remove blank nodes
`LIBXML_NOCDATA` (int)
  Merge CDATA as text nodes
`LIBXML_NOEMPTYTAG` (int)
  Expand empty tags (e.g. `<br/>` to `<br></br>`)

  > 注意:

  > This option is currently just available in the DOMDocument::save and DOMDocument::saveXML functions.

`LIBXML_NOENT` (int)
  Substitute entities
  警告

  Enabling entity substitution may facilitate XML External Entity (XXE) attacks.

`LIBXML_NOERROR` (int)
  Suppress error reports
`LIBXML_NONET` (int)
  Disable network access when loading documents
`LIBXML_NOWARNING` (int)
  Suppress warning reports
`LIBXML_NOXMLDECL` (int)
  Drop the XML declaration when saving a document

  > 注意:

  > Only available in Libxml >= 2.6.21

`LIBXML_NO_XXE` (int)
  Disables XML External Entities (XXE) when performing entity substitution

  > 注意:

  > Only available in Libxml >= 2.13.0, as of PHP 8.4.0

`LIBXML_NSCLEAN` (int)
  Remove redundant namespace declarations
`LIBXML_PARSEHUGE` (int)
  Sets XML_PARSE_HUGE flag, which increases some hardcoded limits from the parser. This affects limits like maximum depth of a document or the entity recursion, as well as limits of the size of text nodes.
  警告

  Because this increases the hardcoded limits, it should only be used with trusted data. Raising the depth limit on untrusted input can lead to excessive resource consumption, such as a stack overflow while processing a deeply nested document.

  > 注意:

  > Only available in Libxml >= 2.7.0 (as of PHP >= 5.3.2 and PHP >= 5.2.12)

`LIBXML_PEDANTIC` (int)
  Sets XML_PARSE_PEDANTIC flag, which enables pedantic error reporting.

  > 注意:

  > Available as of PHP >= 5.4.0

`LIBXML_RECOVER` (int)
  Enables recovery mode when parsing a document.

  > 注意:

  > Only available as of PHP 8.4.0

`LIBXML_XINCLUDE` (int)
  Perform XInclude substitution (only for pull parsers, i.e. XMLReader).
`LIBXML_ERR_ERROR` (int)
  A recoverable error
`LIBXML_ERR_FATAL` (int)
  A fatal error
`LIBXML_ERR_NONE` (int)
  No errors
`LIBXML_ERR_WARNING` (int)
  A simple warning
`LIBXML_VERSION` (int)
  libxml version like 20605 or 20617
`LIBXML_DOTTED_VERSION` (string)
  libxml version like 2.6.5 or 2.6.17
`LIBXML_SCHEMA_CREATE` (int)
  Create default/fixed value nodes during XSD schema validation

  > 注意:

  > Only available in Libxml >= 2.6.14 (as of PHP >= 5.5.2)

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