[regexp] Word boundary

[acid]

How to build the following regexp using PHP preg_match(...) ?

Match all characters beginning from position 0, maximum N characters and aligned to word boundary. So total number of characters will be N + number of characters used to align to word boundary. Text is multiline.

[acid]

it was

PHP Code:

preg_match("/\A(.{1,150}.*?)\b/s", $fullcontent, $smallcontent);