Linking

External links

External links can be created with the default markdown syntax [text](url). Additionally Paradox introduces @link: which accepts the open=new attribute to make the link open in a new browser tab (it adds target="_blank" rel="noopener noreferrer" to the anchor tag), and the title attribute to be used on the a tag.

See the @link:[Paradox GitHub repo](https://github.com/lightbend/paradox) { open=new } for more information.

@ref link

Paradox extensions are designed so the resulting Markdown is Github friendly. For example, you might want to link from one document to the other, let’s say from index.md to setup/index.md.

See @ref:[Setup](setup/index.md) for more information.

This will render to be setup/index.html in the HTML, but the source on Github will link correct as well!

Parameterized links

Parameterized link directives help to manage links that references external documentation, such as API documentation or source code. The directives are configured via base URLs defined in paradoxProperties:

paradoxProperties in Compile ++= Map(
  "github.base_url" -> s"https://github.com/lightbend/paradox/tree/${version.value}",
  "scaladoc.akka.base_url" -> s"http://doc.akka.io/api/${Dependencies.akkaVersion}",
  "extref.rfc.base_url" -> "http://tools.ietf.org/html/rfc%s"
)

After which the directives can be used as follows:

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and
"OPTIONAL" in this document are to be interpreted as
described in @extref[RFC 2119](rfc:2119).

...

Use a @scaladoc[Future](scala.concurrent.Future) to avoid that long
running operations block the @scaladoc[Actor](akka.actor.Actor).

...

Issue @github[#1](#1) was fixed in commit @github[83986f9](83986f9).
See @github[example](/src/test/scala/ServerSetup.scala) { #ssl-setup } for more info.

NOTE: Only use these directives if standard Markdown and @ref does not work, since GitHub won’t preview them correctly.

@scaladoc directive

Use the @scaladoc directives to link to Scaladoc sites based on the package prefix. Scaladoc URL mappings can be configured via the properties scaladoc.<package-prefix>.base_url and the default scaladoc.base_url. The directive will match the link text with the longest common package prefix and use the default base URL as a fall-back if nothing else matches.

For example, given:

• scaladoc.akka.base_url=http://doc.akka.io/api/akka/2.4.10
• scaladoc.akka.http.base_url=http://doc.akka.io/api/akka-http/10.0.0

Then @scaladoc[Http](akka.http.scaladsl.Http$) will resolve to http://doc.akka.io/api/akka-http/10.0.0/akka/http/scaladsl/Http$.html. To link to a package page append .index for Scala 2.12 and .package for Scaladoc generated with versions earlier than 2.12, for example @scaladoc[scaladsl package](akka.http.scaladsl.index) will resolve to http://doc.akka.io/api/akka-http/10.0.0/akka/http/scaladsl/index.html.

By default, scaladoc.scala.base_url is configured to the Scaladoc associated with the configured scalaVersion. If the sbt project’s apiURL setting is configured, it is used as the default Scaladoc base URL.

The @scaladoc directive also supports site root relative base URLs using the .../ syntax.

The directive will identify inner classes and resolve a reference like @scaladoc[Consumer.Control](akka.kafka.scaladsl.Consumer.Control) to https://doc.akka.io/api/alpakka-kafka/current/akka/kafka/scaladsl/Consumer$$Control.html. This is working fine as long as all (sub)package names are starting with a lowercase character while class names start with an uppercase character – which is most often the case.

In a situation where a (sub)package name starts with an uppercase character the reference is resolved incorrectly. This can be fixed by configuring the properties scaladoc.<package-prefix>.package_name_style or the default scaladoc.package_name_style and set it to startWithAnycase. The directive will match the link text with the longest common package prefix and use the default style as a fall-back if nothing else matches. Keep in mind that the OuterClass.InnerClass notation is no longer working then and has to be replaced by OuterClass$$InnerClass.

For example, given:

paradoxProperties in Compile ++= Map(
  //...
  "scaladoc.com.example.package_name_style" -> s"startWithAnycase"
)

 @scaladoc[SomeClass](com.example.Some.Library.SomeClass)
 @scaladoc[Outer.Inner](com.example.Some.Library.Outer$$Inner)
 @scaladoc[Consumer.Control](akka.kafka.scaladsl.Consumer.Control)

Then all are being resolved to the correct URL.

@javadoc directive

Use the @javadoc directives to link to Javadoc sites based on the package prefix. Javadoc URL mappings can be configured via the properties javadoc.<package-prefix>.base_url and the default javadoc.base_url. The directive will match the link text with the longest common package prefix and use the default base URL as a fall-back if nothing else matches.

For example, given:

javadoc.akka.base_url=http://doc.akka.io/japi/akka/2.4.10
javadoc.akka.link_style=frames
javadoc.akka.http.base_url=http://doc.akka.io/japi/akka-http/10.0.0
javadoc.akka.http.link_style=frames

Then @javadoc[Http](akka.http.javadsl.Http#shutdownAllConnectionPools--) will resolve to http://doc.akka.io/japi/akka-http/10.0.0/?akka/http/javadsl/Http.html#shutdownAllConnectionPools--.

Since Java 9 the API documentation from Javadoc doesn’t use frames anymore. Links to classes need to include the class as part of the URI. To choose the link style for the Javadoc-generated API to link to, set the javadoc.<package>.link_style to direct.

The root default, javadoc.base_url is configured to be frames (Javadoc < 9 style).

By default, javadoc.java.base_url is configured to the Javadoc associated with the java.specification.version system property.

The @javadoc directive also supports site root relative base URLs using the .../ syntax.

The directive will identify inner classes and resolve a reference like @javadoc[Flow.Subscriber](java.util.concurrent.Flow.Subscriber) to https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/concurrent/Flow.Subscriber.html. This is working fine as long as all (sub)package names are starting with a lowercase character while class names start with an uppercase character – which is most often the case.

In a situation where a (sub)package name starts with an uppercase character the reference is resolved incorrectly. This can be fixed by configuring the properties javadoc.<package-prefix>.package_name_style or the default javadoc.package_name_style and set it to startWithAnycase. The directive will match the link text with the longest common package prefix and use the default style as a fall-back if nothing else matches. Keep in mind that the OuterClass.InnerClass notation is no longer working then. In this case the class has to be referenced as OuterClass$$InnerClass which is being resolved back to the .-notation.

For example, given:

paradoxProperties in Compile ++= Map(
  //...
  "javadoc.com.example.package_name_style" -> s"startWithAnycase"
)

 @javadoc[SomeClass](com.example.Some.Library.SomeClass)
 @javadoc[Outer.Inner](com.example.Some.Library.Outer$$Inner)
 @javadoc[outer.Inner](com.example.Some.Library.outer$$Inner)
 @javadoc[Outer.inner](com.example.Some.Library.Outer$$inner)
 @javadoc[Consumer.Control](akka.kafka.scaladsl.Consumer.Control)

Then all are being resolved to the correct URL.

@github directive

Use the @github directive to link to GitHub issues, commits and files. It supports most of GitHub’s autolinking syntax.

The github.base_url property must be configured to use shorthands such as #1. To link to a directory or file in a specific version, set the base URL to a tree revision, for example: https://github.com/lightbend/paradox/tree/v0.2.1.

If the sbt project’s scmInfo setting is configured and the browseUrl points to a GitHub project, it is used as the GitHub base URL. Note that this behaviour only occurs if github.base_url is not set so you still have the option to define github.base_url if this is not desirable.

Relative as well as absolute file and directory paths use the value of the github.root.base_dir property to resolve the absolute project path. The sbt plugin automatically sets this property to the absolute path of the root project.

Links to a specific line or line range in a file can use snippet labels to ensure that line numbers are up-to-date. Example:

@github[../../resources/build.sbt] { #setup_example }

@extref directive

Use the @extref directive to link to pages using custom URL templates. URL templates can be configured via extref.<scheme>.base_url and the template may contain one %s which is replaced with the scheme specific part of the link URL. For example, given the property:

extref.rfc.base_url=http://tools.ietf.org/html/rfc%s

then @extref[RFC 2119](rfc:2119) will resolve to the URL http://tools.ietf.org/html/rfc2119.

The @extref directive also supports site root relative base URLs using the .../ syntax.

image.base_url

When placing images via the standard markdown image syntax you can refer to a configured base URL by starting the image href with .../, e.g. like this:

![logo](.../logo.png)

The ... prefix refers to a defined a image.base_url property that is specified either in the page’s front matter or globally like this (for example):

paradoxProperties in Compile ++= Map("image.base_url" -> ".../assets/images")

If the image base URL itself starts with three dots (...) then these in turn refer to the root URL of the site.

Note: Using this feature will not allow GitHub to preview the images correctly on the web.