Currently, only user-defined fields are supported as placeholders. But there are some more possible in LibreOffice und Apache OpenOffice.
<text:p text:style-name="P1">
User-Defined-Fields:
<text:user-field-get text:name="CUST_FORENAME">John</text:user-field-get>
</text:p>
<text:p text:style-name="P1">
Real placeholders:
<text:line-break/>
<text:placeholder text:placeholder-type="text"><CUST_LASTNAME></text:placeholder>
<text:line-break/>
<text:placeholder text:placeholder-type="text" text:description="CustomerNumber"><CUST_NUMBER></text:placeholder>
</text:p>
<text:p text:style-name="Normal">
<text:span text:style-name="T2">
Customer last name and forename:
<text:s/>
</text:span>
<text:database-display text:column-name="CUST_LASTNAME" text:table-type="table" text:table-name=""/>
<text:span text:style-name="T3">
,
<text:s/>
</text:span>
<text:database-display text:column-name="CUST_FORENAME" text:table-type="table" text:table-name=""/>
</text:p>