【応用編】bootstrap Checkboxes and radios + Collapse
bootstrapの Collapse をradio（あるいはCheckbox）で。
具体的には、送信フォームでradio（あるいはCheckbox）で選択してCollapseを使う、というものです。
checkbox
<form>
<div class="form-group">
<div class="form-check">
<input class="form-check-input" type="checkbox" value="" id="defaultCheck1">
<label class="form-check-label" for="defaultCheck1">
Default checkbox1
</label>
</div>
<div class="form-check">
<input class="form-check-input" type="checkbox" data-toggle="collapse" data-target="#collapseExample" aria-expanded="false" aria-controls="collapseExample" value="" id="defaultCheck2">
<label class="form-check-label" for="defaultCheck2">
Disabled checkbox2
</label>
</div>
<div class="collapse mt-2" id="collapseExample">
<div class="card card-body">
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</div>
</div>
</div>
</form>
radio
<form>
<div class="form-group">
<div class="form-check">
<input class="form-check-input" type="radio" data-toggle="collapse" data-target="#collapseTwo.show" name="exampleRadios" id="exampleRadios1" value="option1">
<label class="form-check-label" for="exampleRadios1">
Default radio1
</label>
</div>
<div class="form-check">
<input class="form-check-input" type="radio" data-toggle="collapse" data-target="#collapseTwo.show" name="exampleRadios" id="exampleRadios2" value="option2">
<label class="form-check-label" for="exampleRadios2">
Second default radio2
</label>
</div>
<div class="form-check">
<input class="form-check-input" type="radio" data-toggle="collapse" data-target="#collapseTwo:not(.show)" aria-expanded="true" aria-controls="collapseTwo" name="exampleRadios" id="exampleRadios3" value="option3">
<label class="form-check-label" for="exampleRadios3">
third default radio3
</label>
</div>
<div class="collapse mt-2 collapseTwo" id="collapseTwo">
<div class="card card-body">
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</div>
</div>
</div>
</form>
data-target=”#collapseTwo.show”
data-target=”#collapseTwo:not(.show)”
# ～ の部分はIDでもclassでもOKです。
classを使う場合は、
data-target=”.collapseTwo.show”
data-target=”.collapseTwo:not(.show)”