웹에서 요소 복사. HTML DOM execCommand() Method
현재 선택영역의 텍스트를 인자로 받은 값을 통해 변환시킵니다. 
execCommand 에서 "copy" 명령 사용
document.execCommand('Italic')           // 기울이기
document.execCommand('Underline')        // 밑줄
document.execCommand('StrikeThrough')    // 중간줄
document.execCommand('Cut')              // 자르기
document.execCommand('Copy')             // 복사하기
document.execCommand('Paste')            // 붙혀넣기
document.execCommand('Undo')             // 실행취소
document.execCommand('Redo')             // 다시실행
document.execCommand('insertorderedList')    // 글번호 매기기
document.execCommand('insertunorderdList')   // 글머리 매기기
document.execCommand('outdent')          // 내어쓰기
document.execCommand('indent')           // 들여쓰기
document.execCommand('justifyleft')      // 왼쪽정렬
document.execCommand('justifycenter')    // 가운데정렬
document.execCommand('justifyright')     // 오른쪽정렬
Syntax
document.execCommand(command, showUI, value)
Parameter Values
ValueDescription
| command | Specifies the name of the command to execute on the selected section. 
 Legal values:
 "backColor"
 "bold"
 "createLink"
 "copy"
 "cut"
 "defaultParagraphSeparator"
 "delete"
 "fontName"
 "fontSize"
 "foreColor"
 "formatBlock"
 "forwardDelete"
 "insertHorizontalRule"
 "insertHTML"
 "insertImage"
 "insertLineBreak"
 "insertOrderedList"
 "insertParagraph"
 "insertText"
 "insertUnorderedList"
 "justifyCenter"
 "justifyFull"
 "justifyLeft"
 "justifyRight"
 "outdent"
 "paste"
 "redo"
 "selectAll"
 "strikethrough"
 "styleWithCss"
 "superscript"
 "undo"
 "unlink"
 "useCSS"
 | 
| showUI | A Boolean, specifies if the UI should be shown or not | 
| value | Some commands need a value to be completed |