Not sure this is a bug; will post it anyway.
I added a Codemirror field on my form but it doesn't show the "description" of each option. You can reproduce it in Nexus -> Products -> Custom Fields -> Email content for after purchase.
$form->add( new \IPS\Helpers\Form\Codemirror( "p_email_{$k}_html", $this->$valueKey, FALSE, array(
'preview' => \IPS\Http\Url::internal('app=nexus&module=store&controller=packages&do=emailPreview')->csrf(),
'tags' => array(
'{$purchase->name}' => \IPS\Member::loggedIn()->language()->addToStack('ps_name'),
'{$purchase->expires}' => \IPS\Member::loggedIn()->language()->addToStack('p_email_tag_expire'),
'{$purchase->renewals}' => \IPS\Member::loggedIn()->language()->addToStack('ps_renewals'),
'{$purchase->custom_fields[1]}' => \IPS\Member::loggedIn()->language()->addToStack('p_email_tag_field'),
'{$purchase->url()}' => \IPS\Member::loggedIn()->language()->addToStack('p_email_tag_url'),
'{$purchase->licenseKey()->key}' => \IPS\Member::loggedIn()->language()->addToStack('license_key'),
)
), NULL, NULL, NULL, "p_email_{$k}_html" ) );
Every option has its "description" but it doesn't show in the form:
The value of each language bit should be displayed in the yellow area above.