[xsl] How to produce X when an attribute of an element does not exist or equals Y?

[Joyce Celeste Chapman <chapmajc@xxxxxxxxxxxxx>]

Hi, I'm new to the listserv and to XSL. Using the XML below and XSLT 
1.0, I would like content to appear both when an attribute of an 
element does not exist and when it equals X. Specifically, I would like 
the contents of data-field tag 555 to appear if this data-field does 
not have any "ind1" attribute, or if its ind1 equals 8.

Data fields with indicators versus no indicators in my XML look like this:
<data-field tag="555" ind1="0">
   <subfield code="a">...</subfield>
</data-field>
<data-field tag="555">
   <subfield code="a">...</subfield>
</data-field>

This is the XSLT I have figured out, minus the missing part:
<xsl:if test="data-field[@tag='555'][@ind1='8'] | ...or if a data-field 
with attribute 555 has no attribute ind1">
   <otherfindaid encodinganalog="555">
       <xsl:for-each select="data-field[@tag='555'][@ind1='8'] | ...or 
if a data-field with attribute 555 has no attribute ind1">
           <p>
               <xsl:value-of select="."/>
           </p>
       </xsl:for-each>
   </otherfindaid>
</xsl:if>

I would be very grateful for any help. Thank you!