<span tal:define="global true python:1; global false python:0" />

<img ismap>
<img ismap=ismap>
<img ismap="ismap">
<img ismap="foo">

<img ismap tal:attributes="ismap true">
<img ismap tal:attributes="ismap false">
<img ismap tal:attributes="ismap nothing">

<img ismap="foo" tal:attributes="ismap true">
<img ismap="foo" tal:attributes="ismap false">
<img ismap="foo" tal:attributes="ismap nothing">

<img tal:attributes="ismap true">
<img tal:attributes="ismap false">
<img tal:attributes="ismap nothing">

<span tal:define="global x string:x.gif" />

<img src="foo">
<img src="foo" tal:attributes="src x">
<img src="foo" tal:attributes="src nothing">