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= Java System Properties Affecting Ivy

== XML Parser Settings

Starting with Ivy 2.5.2 Ivy's XML parser can be controlled via the use
of two newly introduced system properties.

If you want to restore the default behavior of Ivy 2.5.1 and earlier
you need to set `ivy.xml.allow-doctype-processing` to `true` and
`ivy.xml.external-resources` to `ALL`.

=== `ivy.xml.allow-doctype-processing`

This system property accepts `true` or `false` as values. When set to
`false` Ivy will not allow any processing of doctype declarations at
all, while setting it to `true` enables it.

The default is to allow doctype processing if and only if Ivy is
parsing a Maven POM file.

=== `ivy.xml.external-resources`

This system property controls if external resources are read during
doctype processing - and if so, where they can be loadad from. The
value of this system property is only ever used if
`ivy.xml.allow-doctype-processing` is not `false`.

The accepted values are

* `PROHIBIT` makes Ivy fail if any doctype tries to load an external
  resource.
* `IGNORE` makes Ivy ignore any external resource that the doctype
  declaration wants to load.
* `LOCAL_ONLY` allows external resources to be loaded via `file:` or
  `jar:file` URIs only.
* `ALL` allows external resources to be loaded from any URI.

The default behavior is to not allow doctype processing at all, but if
it is enabled the value `PROHIBIT` is assumed unless the property has
been set explicitly.

When reading Maven POMs a specific internal system id is recognized as
resource and will be loaded from a resource shipping with the Ivy
distribution in order to deal with invalid POM files accepted by
Apache Maven - and the default value for this property is
`IGNORE`in that case. See
link:https://issues.apache.org/jira/browse/IVY-921[IVY-921] for
details.