ドロップダウンのリスト部分を強制的に表示します。
ドロップダウン (PRIM_MD.Dropdown) のメンバ
The OpenDropDown method provides programmatic control over the drop down list portion of the drop down. This is useful when using the drop down as a means of data entry and you wish to open and close the drop down to show previously entered values.
EPC142030 February 2019