What are tag comments good for in pom.xml?

Question

I'm currently going through https://spring.io/guides/gs/maven/#scratch and I just found

<dependencies>
    <!-- tag::joda[] -->
    <dependency>
        <groupId>joda-time</groupId>
        <artifactId>joda-time</artifactId>
        <version>2.9.2</version>
    </dependency>
    <!-- end::joda[] -->
    <!-- tag::junit[] -->
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
        <scope>test</scope>
    </dependency>
    <!-- end::junit[] -->
</dependencies>

and I wonder:

What is <!-- tag::joda[] --> good for?

Answer 1

The Getting Started Guide you are reading, is generated from an AsciiDoc file:

https://github.com/spring-projects/spring-boot/blob/master/README.adoc

AsciiDoc is a document format equivalent to DocBook XML. Instead of copy-pasting part of the source code, the AsciiDoc syntax allows to point to some parts of the source code.

To include a part of the pom.xml you can use the following syntax:

include::complete/pom.xml[tag=joda]

which will include the snippet:

<!-- tag::joda[] -->
<dependency>
    <groupId>joda-time</groupId>
    <artifactId>joda-time</artifactId>
    <version>2.9.2</version>
</dependency>
<!-- end::joda[] -->

To answer you question, <!-- tag::joda[] --> is a marker allowing AsciiDoc to extract a part of the file and inserting it into the getting started guide.