Question: What year did a demo of the song leak?
About the article "Part of Me (Katy Perry song)", section "Abstract".

Candidate passages:
 Demo (music), a song recorded for reference rather than release "Demo" (Behind Crimson Eyes), a 2004 recording by the band Behind Crimson Eyes "Demo" (Deafheaven album), a 2010 EP by Deafheaven "Demo" (The Flatliners Album), a 2002 album by the band The Flatliners "Demo" (Miss May I album), a 2008 recording by the metalcore band Miss May I "Demo", a 1990 single by Die Krupps "Demo" (P-MODEL), a 1979 recording by songwriters Susumu Hirasawa and Yasumi Tanaka "Demo (Skinless)", a 1994 recording by the band Skinless "Demo 2004" (Year of No Light album), a 2004 recording by Year of No Light "Demo #2", an unreleased recording by Neutral Milk Hotel  
  "King And Queen of England" (demo with piano introduction)  "Rising For the Moon" (demo)  "One More Chance" (demo)  "King and Queen of England" (take 1, demo)  "After Halloween" (demo 1974)  "What Is True" (demo)  "Stranger to Himself" (demo)  "Take Away the Load" (demo)  "By the Time It Gets Dark" (demo)  "I’m a Dreamer" (demo)  "Full Moon" (demo)  "Take Me Away" (demo)  "All Our Days" (demo)  "No More Sad Refrains" (demo)  "Still Waters Run Deep" (demo)  "One Way Donkey Ride" (demo)  "I’m a Dreamer" (2nd demo)  "Full Moon" (2nd demo)  "Makes Me Think of You" (demo)  
After returning from a vacation on Tahiti, Clarkson found out over 50 of her newly recorded demo material were leaked online, including "Stronger".
She commented that the leak felt worse than being physically robbed.
In an attempt to counter-attack the leakage, RCA finally debuted the song online on October 5, 2011, three weeks ahead of the album's release.
An acoustic version of the song appears in Clarkson's second extended play, "iTunes Session".
"Stronger" was officially released as the album's second single to mainstream radio on January 17, 2012.
A dance remixes of the song were made available on February 3, 2012.
On February 17, 2012, it was released as a CD single. 
The lyrics of the song discuss Gaga's artistry and the way she expresses herself.
She reasserts her agency as a female, a human being, and as someone who owns her own sexuality.
Gaga confessed that she does not wear the burqa as a political statement, but rather because she feels she identifies with others who wear a burqa.
She concludes the song chanting the name of the parent album, "Artpop".
The song leaked early on before the release of the album, and led many to believe that it was a final album edit, but Gaga confirmed that the leak was simply a demo.
"Aura" was in consideration as the second single from "Artpop", when Gaga released a poll, asking fans what song they'd rather have released as single, in which "Aura" won; however, "Venus" was chosen instead by Gaga herself.
Gaga confirmed that it would serve as a promotional single instead, although plans on making it a single in the future. 
  "Jane Says (Radio Tokyo Demo)" *  "Pigs in Zen (Radio Tokyo Demo)"  "Mountain Song (Radio Tokyo Demo)"  "Had a Dad (Radio Tokyo Demo)"  "I Would for You (Radio Tokyo Demo)"  "Idiots Rule (Demo)" *  "Classic Girl (Demo)" *  "Up the Beach (Demo)" *  "Suffer Some (Demo)" *  "Thank You Boys (Demo)" *  "Summertime Rolls (Demo)" *  "City (Demo)" *  "Ocean Size (Demo)" *  "Stop!
(Demo)" *  "Standing in the Shower...
Thinking (Demo)" *  "Ain't No Right (Demo)" *  "Three Days (Demo)" *