ensureLinePrefix prefix [prefix-to-add] text

ensureLinePrefix ensures that each line of text starts with prefix. If any line does not start with prefix then prefix-to-add is prepended to that line.

Typically, ensureLinePrefix is used to ensure that lines are commented out, similar to the comment template function. ensureLinePrefix only modifies lines that are not already comments, whereas comment modifies all lines, even if they are already comments.

!!! example

```
{{ "### Heading\nBody\n" | ensureLinePrefix "#" }}
{{ "### Heading\nBody\n" | ensureLinePrefix "#" "# " }}
```