Parsing "its": possessive form of it

[Andrey]

tell application "System Events" 
tell (application process "Filemaker Pro" of application "System Events") to set it's frontmost to true --ok
tell (application process "Filemaker Pro" of application "System Events") to set its frontmost to true --its not parsed
end tell

[Andrey]

http://www.businesswritingblog.com/business_writing/2006/05/its_its_or_its_.html

Its is like hers, his, ours, theirs, and yours. These are all pronouns. Possessive pronouns do not have apostrophes. That is because their spelling already indicates a possessive. For example, the possessive form of she is hers. The possessive form of we is ours. Because we change the spelling, there is no need to add an apostrophe to show possession. Its follows that pattern.