Entity not what XPath knows - it's best to use its equivalent (self-   ) symbol object  
To select all td top element - table , which do not contain use :
/table/tr/td[not(contains(., ' '))]
To select all rows in this table so that none of their children td contain use :
/table/tr[not(td[contains(., ' ')])]
To select all td children of all rows in this table so that none of their children td contain use :
/table/tr[not(td[contains(., ' ')])]/td
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