The web.xml validation of TomEE/TomEE+ doesn't behaves like Tomcat 7.0.27's when there is a white space in the load-on-startup value of a servlet declaration, like this one:
<load-on-startup> 1 </load-on-startup>
In this case, the web application is not registered by TomEE+, and have this stack trace in catalina.out:
Caused by: org.apache.tomee.catalina.TomEERuntimeException: org.apache.openejb.OpenEJBException: Cannot unmarshall the web.xml file: file:/app/apache-tomee-webprofile-1.0.0/webapps/myApp/WEB-INF/web.xml: java.lang.NumberFormatException: For input string: " 1 "
Please note that the problem was reproduced with Apache TomEE+ 1.0.0 on Windows with 64-bit JDK 7 update 7 on Windows 2008 R2 SP1.
Please also note that the web application was based on Servlet 2.5 level of compliance.
Using the same operating system & JDK version, there is not such issue with Tomcat 7.0.27.
Also this issue cannot be reproduce using IBM WebSphere 184.108.40.206 or ORACLE WebLogic 12x.
I don't know what Servlet 2.5 specification says about load-on-startup values, but the impact of this TomEE/TomeEE+ behaviour is that some applications running on Tomcat / WebSphere / WebLogic cannot be deployed Out Of The Box, which may slow down TomEE adoption.
As such, I don't think it's a minor issue. But we never know, perhaps TomEE developers will says that TomEE is strictly implementing Servlet specification and other app servers don't