Both the above probably are good advice.
However, to be fair, I took the train from Istanbul to Aleppo and the only people they were worried about were Iraqis. I'd bought the Israel guide in Istanbul and remembered such scare stories midway on the train, but decided that throwing out of the window would make me a loon. So put at bottom of the bag and decided to rely on a winning smile if went pear shaped. Was all fine.
Didn't get impression i was particularly lucky at the border not to be searched ... It's Syria ... They are not being paid to search backpacks of travellers who want to go there lol. They don't really care at the train stops. And if I had to compare relaxed and polite border control at the Turkish border with JFK ... yeah, US customs are the worst advert for a country in the world.
On other hand, airport maybe different. Been to Beirut airport and they have 2 guys on gate checking passports twice just to see you haven't been to Israel. It's clearly not to check you are a terrorist ... as that will hardly get you barred from the country.
Anyway, didn't find the ME book sufficient frankly, but the LP individual guides fine. If you really worried buy in Tel Aviv.
Just enjoy both Tel Aviv and Damascus. Both great. But TA more so.