Example

$form = new Form('plugins-dependent-fields-form-1', 'horizontal');

$form->addOption('subject', '', 'Your request concerns:');
$form->addOption('subject', 'Support', 'Support');
$form->addOption('subject', 'Other', 'Other');
$form->addHelper('if other, please tell us more', 'subject');
$form->addSelect('subject');

$form->startDependentFields('subject', 'Other');
$form->addInput('text', 'request-more', '', '', 'required, placeholder=Please tell more about your request ...');
$form->endDependentFields();

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if other, please tell us more
<div class="row mb-3">
	<div class="col-sm-offset-4 col-sm-8">
		<select id="subject" name="subject"  class="form-select">
			<option value="" >
				Your request concerns:
				</option>
					<option value="Support" >
						Support
						</option>
							<option value="Other" >
								Other
								</option>
									</select>
										<span class="form-text" id="subject-helper">if other, please tell us more</span>
										</div>
											</div>
												<div class="hidden-wrapper off" data-parent="subject" data-show-values="Other" data-inverse="">
													<div class="row mb-3">
														<div class="col-sm-offset-4 col-sm-8">
															<input id="request-more" name="request-more" type="text" value="" required placeholder="Please tell more about your request ..." class="form-control" aria-label="Please tell more about your request ...">
															</div>
																</div>
																	</div>