ZWJ as a Ligature Suppressor

[Richard Wordingham]

According to the text just after TUS 7.0.0 Figure 23-3
(http://www.unicode.org/versions/Unicode7.0.0/ch23.pdf#G25237), ZWJ
suppresses ligatures in Arabic script.  Does this rule apply to other
normally cursive joined scripts, e.g. Syriac and Mongolian?

Am I right in thinking that for an OpenType font for other scripts, the
font writer must take precautions to prevent ZWJ accidentally
suppressing ligatures that would be better suppressed by ZWNJ or <ZWJ
ZWNJ ZWJ>?