Exception in commented line O_o - grails

Question

I have this:
<!-- <div class="fieldcontain ${hasErrors(bean: azafataInstance, field: 'localidad', 'error')} required" style="margin-left: 10px">-->
<!--<label for="localidad">Localidad</label> -->
<!--<g:if test="${params?.localidad }">-->
<!--<g:select id="localidad" title="${g.message(code: 'infoPersonal.localidad')}" name="localidad" value="${params?.localidad}" from="${[' ',params.localidad]}" noSelection="${['':message(code:'localidadSelect')]}" onClick="this.style.color='black'" onFocus="this.style.color='black'" style="max-width:168px" />-->
<!--</g:if>-->
<!--<g:else>-->
<!--<g:select id="localidad" title="${g.message(code: 'infoPersonal.localidad')}" name="localidad" value="${params?.localidad}" from="${['']}" noSelection="${['':message(code:'localidadSelect')]}" onClick="this.style.color='black'" onFocus="this.style.color='black'" style="max-width:168px" />-->
<!--</g:else>-->
<!--</div>-->
As you can see... lines are commented. I run the project and i got this:
URI
/com.publidirecta.azafatas/azafataCertificada/registro_page
Class
org.codehaus.groovy.grails.web.taglib.exceptions.GrailsTagException
Message
Tag [else] cannot have non-whitespace characters directly preceding it.
Around line 95 of grails-app/views/azafataCertificada/registro.gsp
92:<!--<g:if test="${params?.localidad }">-->
93:<!--<g:select id="localidad" title="${g.message(code: 'infoPersonal.localidad')}" name="localidad" value="${params?.localidad}" from="${[' ',params.localidad]}" noSelection="${['':message(code:'localidadSelect')]}" onClick="this.style.color='black'" onFocus="this.style.color='black'" style="max-width:168px" />-->
94: <!--</g:if>-->
95: <!--<g:else>-->
96: <!--<g:select id="localidad" title="${g.message(code: 'infoPersonal.localidad')}" name="localidad" value="${params?.localidad}" from="${['']}" noSelection="${['':message(code:'localidadSelect')]}" onClick="this.style.color='black'" onFocus="this.style.color='black'" style="max-width:168px" />-->
97:<!--</g:else>-->
98:<!--</div>-->
Trace
Line | Method
->> 886 | runTask in java.util.concurrent.ThreadPoolExecutor$Worker
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
| 908 | run in ''
^ 680 | run . . in java.lang.Thread
Caused by GrailsTagException: Tag [else] cannot have non-whitespace characters directly preceding it.
->> 95 | runTask in /grails-app/views/azafataCertificada/registro.gsp
The question is, obviously...
How is it possible, in a decent framework, can a commented line throw an exception!!!

Answer 1

Because <!-- isn't a comment in GSP.
As you have discovered, the GSP parser treats HTML-style comments as normal content, to make it possible to generate output that contains HTML comments such as within script tags
<script type="text/javascript><!--
js goes here;
//--></script>
or IE conditional comments
<!--[if IE 6]>
<script type="text/javascript" src="${resource(dir:'css', file:'ie6-fixup.js')}"></script>
<![endif]-->
The syntax for GSP comments is
<%-- this is commented out --%>
the GSP parser will ignore anything inside this sort of comment.