Check single line is table element

Table is not a just multi line block like others.

Because other multi line blocks prefix is at the first but table is not. And a table requires two essential line

| ex | ex | ex |
| -- | -- | -- |

like above, line with dash and column elements.

if something is missing above essential two line, all other lines must be transformed into single line block. So before implementing table part, check string lines feature is needed