returns how many times each placeholder is present in the document
almost the same code as `getVariables`
useful when cloning a block a number of times and want to replace
placeholders that are present more than once in the block
(using the `$limit` parameter of `setValue`)
it wrongly matched `<w:pPr` when looking for `<w:p`
in that case the cloned block would not be valid XML,
and so the generated docx document could not be opened by Word
adding the `\b` word boundary to the regex fixes this.
the accompanying unit test failed with this message when trying to load
the generated file:
```
ErrorException: DOMDocument::loadXML(): Opening and ending tag mismatch:
p line 2 and body in Entity, line: 2
```
This might solve issues such as #681 and #664.
troosan
Yurii.sio2
Martin Hanzl
Nicolas Dermine
Gabriel Caruso
Roman Syroeshko