Suricata

When backslash is used in "content" it needs to be escaped. If it is not though - there is no err message about what is wrong - just that the rule fails to load.
It would be helpful to have a descriptive msg about what needs to be improved/escaped in the rule.
The docs do not explicitly mention it needs escaping as a special character either - https://suricata.readthedocs.io/en/latest/rules/payload-keywords.html#content

sudo /opt/suricata-asan/bin/suricata -S unknown.rule  -T --engine-analysis -l log/ 
[17656] 24/9/2018 -- 22:42:17 - (suricata.c:1900) <Info> (ParseCommandLine) -- Running suricata under test mode
[17656] 24/9/2018 -- 22:42:17 - (suricata.c:1084) <Notice> (LogVersion) -- This is Suricata version 4.1.0-dev (rev 8c3f1aa7)
[17656] 24/9/2018 -- 22:42:17 - (detect-engine-loader.c:187) <Error> (DetectLoadSigFile) -- [ERRCODE: SC_ERR_INVALID_SIGNATURE(39)] - error parsing signature "alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"Backslash needs escaping msg"; flow:established,to_server; content:"MyBackslash\here"; sid:86; rev:1; )" from file unknown.rule at line 1
[17656] 24/9/2018 -- 22:42:17 - (detect-engine-loader.c:346) <Warning> (SigLoadSignatures) -- [ERRCODE: SC_ERR_NO_RULES_LOADED(43)] - 1 rule files specified, but no rule was loaded at all!
[17656] 24/9/2018 -- 22:42:17 - (suricata.c:2439) <Error> (LoadSignatures) -- [ERRCODE: SC_ERR_NO_RULES_LOADED(43)] - Loading signatures failed.

cat unknown.rule 
alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"Backslash needs escaping msg"; flow:established,to_server; content:"MyBackslash\here"; sid:86; rev:1; )

content:"MyBackslash\\here";
content:"MyBackslash|5C|here";