migration process plugin not registering My plugin aims to strip out html tags from titles being imported from xml
Here is the error I'm receiving:
FVFXF0ETHV2F:process$ drush mim complinet_xml_to_node
Drupal\Component\Plugin\Exception\PluginNotFoundException: The "stripouthtml" plugin does not exist. in                                          [error]
/Users/Sites/devdesktop/drupal8test/core/lib/Drupal/Component/Plugin/Discovery/DiscoveryTrait.php:52
Stack trace:

Here is the plugin which lives in custom/complinetmigration/src/Plugin/migrate/process

&lt;?php

/**
 * @file
 * Contains \Drupal\complinetmigration\Plugin\migrate\process\StripOutHTML.
 */

namespace Drupal\complinetmigration\Plugin\migrate\process;

use Drupal\migrate\MigrateException;
use Drupal\migrate\MigrateExecutableInterface;
use Drupal\migrate\ProcessPluginBase;
use Drupal\migrate\Row;

 /**
 * @MigrateProcessPlugin(
 * id = "stripouthtml"
 * )
 *
 */
class StripOutHTML extends ProcessPluginBase {

  /**
   * {@inheritdoc}
   */
  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
    // $value: cut off .&lt;nnn&gt;Z and replace by Z
    if( is_null($value) )
    {
      return $value;
    }

    // $old = $value;

    $value= strip_tags($value);
    // drush_print_r( $old . ' -&gt; ' . $value );

    return $value;
  }

}


and here is the migration

# This migration demonstrates importing from a monolithic XML file.
dependencies:
    enforced:
      module:
        - complimentmigration
id: compliment_xml_to_node
label: XML feed of nodes from compliment
migration_group: compliment
migration_tags:
  - advanced xml import
source:
  # We use the XML data parser plugin.
  plugin: url
  data_fetcher_plugin: http
  data_parser_plugin: xml
  # Normally, this is one or more fully-qualified URLs or file paths. Because
  # we can't hardcode your local URL, we provide a relative path here which
  # hook_install() will rewrite to a full URL for the current site.
  urls: private://FINRAManual08-08-18.xml
  #  - /migrate_example_advanced_position?_format=xml
  # Visit the URL above (relative to your site root) and look at it. You can see
  # that &lt;response&gt; is the outer element, and each item we want to import is a
  # &lt;position&gt; element. The item_xpath value is the xpath to use to query the
  # desired elements.
  item_selector: '/quickpipe/section/section/section'
  # Under 'fields', we list the data items to be imported. The first level keys
  # are the source field names we want to populate (the names to be used as
  # sources in the process configuration below). For each field we're importing,
  # we provide a label (optional - this is for display in migration tools) and
  # an xpath for retrieving that value. It's important to note that this xpath
  # is relative to the elements retrieved by item_xpath.
  fields:
    -
      name: versionid
      label: 'Version Id'
      selector: 'version[1]/@recordId'
    -
      name: title
      label: 'Title'
      selector: 'version[1]/title'
    -
      name: content
      lable: 'Content'
      selector: 'version[1]/content'

  # Under 'ids', we identify source fields populated above which will uniquely
  # identify each imported item. The 'type' makes sure the migration map table
  # uses the proper schema type for stored the IDs.
  ids:
    versionid:
      type: integer
destination:
  plugin: entity:node
process:
  # Hardcode the destination node type (bundle) as 'migrate_example_beer'.
  type:
    plugin: default_value
    default_value: article
  title:
    plugin: stripouthtml
    source: title
  uid:
    plugin: default_value
    default_value: 1
  sticky:
    plugin: default_value
    default_value: 0
  body: content
migration_dependencies: {}
The module was in a funky state. I ran drush pm-uninstall complimentmigration which gave the following message.


  complimentmigration is already uninstalled.
  There were no extensions that could be uninstalled.


Then I ran drush en complimentmigration which gave the following message.


  The following extensions will be enabled: complimentmigration
  Do you really want to continue? (y/n): y
  Drupal\Core\Config\PreExistingConfigException: Configuration objects (migrate_plus.migration.compliment_xml_to_node) provided by                      complimenttmigration already exist in active configuration in /Users/Sites/devdesktop/drupal8test/core/lib/Drupal/Core/Config/PreExistingConfigException.php:65
  Stack trace:
  0 /Users/Sites/devdesktop/drupal8test/core/lib/Drupal/Core/Config/ConfigInstaller.php(496): Drupal\Core\Config\PreExistingConfigException::create('complimenttmigrat...', Array)
  1 /Users/Sites/devdesktop/drupal8test/core/lib/Drupal/Core/ProxyClass/Config/ConfigInstaller.php(132): Drupal\Core\Config\ConfigInstaller->checkConfigurationToInstall('module', 'complimentmigrat...')
  2 /Users/Sites/devdesktop/drupal8test/core/lib/Drupal/Core/Extension/ModuleInstaller.php(150): Drupal\Core\ProxyClass\Config\ConfigInstaller->checkConfigurationToInstall('module', 'complimenttmigrat...')
  3 /Users/Sites/devdesktop/drupal8test/core/lib/Drupal/Core/ProxyClass/Extension/ModuleInstaller.php(83): Drupal\Core\Extension\ModuleInstaller->install(Array, true)
  4 /Applications/DevDesktop/tools/vendor/drush/drush/commands/core/drupal/environment.inc(131): Drupal\Core\ProxyClass\Extension\ModuleInstaller->install(Array, true)
  5 /Applications/DevDesktop/tools/vendor/drush/drush/commands/core/drupal/environment.inc(198): drush_module_install(Array)
  6 /Applications/DevDesktop/tools/vendor/drush/drush/commands/pm/pm.drush.inc(1180): drush_module_enable(Array)
  7 /Applications/DevDesktop/tools/vendor/drush/drush/includes/command.inc(422): drush_pm_enable('complimentmigrat...')
  8 /Applications/DevDesktop/tools/vendor/drush/drush/includes/command.inc(231): _drush_invoke_hooks(Array, Array)
  9 /Applications/DevDesktop/tools/vendor/drush/drush/includes/command.inc(199): drush_command('complimentmigrat...')
  10 /Applications/DevDesktop/tools/vendor/drush/drush/lib/Drush/Boot/BaseBoot.php(67): drush_dispatch(Array)
  11 /Applications/DevDesktop/tools/vendor/drush/drush/includes/preflight.inc(66): Drush\Boot\BaseBoot->bootstrap_and_dispatch()
  12 /Applications/DevDesktop/tools/vendor/drush/drush/drush.php(12): drush_main()
  13 {main}


I ran drush ev "\Drupal::service('config.manager')-&gt;uninstall('module', 'complimentmigration');", followed by drush en complimentmigration, which gave the following message.


  The following extensions will be enabled: complimentmigration
  Do you really want to continue? (y/n): y
  complimentmigration was enabled successfully.      


This fixed the issue I had.