And you've tried:
<Page Location="135,0" Name="BestowalOfVitaePage" ScrollExtent="27,27" Size="27,27">
<Button LocalTooltip="reactive heal" Name="BestowalOfVitaeButton" OnPress="target_none
target_self
useability `Supplicant's Prayer`" Opacity="0.000" ScrollExtent="27,27" Size="27,27"></Button>
<Icon IconRect="209,0,252,39" IconResource="images/icons/icon_ss6.dds" Name="BestowalOfVitaeIcon" ScrollExtent="27,27" Size="27,27" TreatAsButton="true"/>
</Page>
That might work. Extra " shouldn't work because they're closing the string at the start (since they were used to start it in the first place) but the back apostrophe should serve as a text delimiter to say `Supplicant's Prayer` is one whole string.
If not you could try doing something like OnHover="A=Supplicant's Prayer
OnPress=OnPress="target_none
target_self
useability " ## A
That may work, but my brain is still a bit sleep befuddled so not 100% sure on the coding.