文書のメタデータを返すJSONメソッド。
このメソッドは、JSONオブジェクトを次の形式で返します。
{
“size”: Total uncompressed size of the document.
“depth”: Levels of nesting (starts at 1).
“keycnt”: Number of keys.
“objcnt”: Number of values that are Objects.
“arycnt”: Number of values that are Arrays.
“strcnt”: Number of values that are Strings.
“nbrcnt”: Number of values that are Numbers.
“boolcnt”: Number of values that are “true” or “false”.
“nullcnt”: Number of values that are “null”.
“keylen”: Minimum, maximum, and average number of characters in the keys.
}