Issue #2845492 by quietone, FJ7, phenaproxima: Add documentation to SkipRowifNotSet process plugin

core/modules/migrate/src/Plugin/migrate/process/SkipRowIfNotSet.php

@@ -8,9 +8,30 @@
 use Drupal\migrate\MigrateSkipRowException;
 
 /**
- * If the source evaluates to empty, we skip the current row.
+ * Skips processing the current row when a source value is not set.
  *
- * @link https://www.drupal.org/node/2345935 Online handbook documentation for skip_row_if_not_set process plugin @endlink
+ * The skip_row_if_not_set process plugin checks whether a value is set. If the
+ * value is set, it is returned. Otherwise, a MigrateSkipRowException
+ * is thrown.
+ *
+ * Available configuration keys:
+ *   - index: The source property to check for.
+ *
+ * Example:
+ *
+ * @code
+ *  process:
+ *    settings:
+ *      # Check if the "contact" key exists in the "data" array.
+ *      plugin: skip_row_if_not_set
+ *      index: contact
+ *      source: data
+ * @endcode
+ *
+ * This will return $data['contact'] if it exists. Otherwise, the row will be
+ * skipped.
+ *
+ * @see \Drupal\migrate\Plugin\MigrateProcessInterface
  *
  * @MigrateProcessPlugin(
  *   id = "skip_row_if_not_set",