Cinco de Mayo--Fifth of May--is a holiday celebrating the Mexican victory over the French in the 1862 battle known as the Battle of Puebla or the Battle of Cinco de Mayo. Usually, the celebrations and commemorations of a war or battle are classed in the 900s. For example, use 940.546 Celebrations, commemorations, memorials of World War II for comprehensive works on World War II commemorations, 940.5421421 for commemorations of the Normandy Invasion. If there is not a specific development given in the 900s, celebrations and commemorations can be shown by adding notation 6 Celebrations, commemorations, memorials (from the add table at 940-990) to designated numbers. If one cannot use the notation from the add table at a particular number, the celebration is classed at the number for the battle. Thus, a work that focuses on the Battle of Puebla is classed with Mexican history in 972.07 Period of European intervention, 1861-1867.
When the celebration becomes a patriotic holiday, comprehensive works on the celebration are classed in 394.26 Holidays. Cinco de Mayo is now a holiday in the state of Puebla and other parts of Mexico. In the United States, it is a celebration of Mexican culture, food, music, beverage, and customs unique to Mexico. Thus, the holiday is classed in 394.262 Holidays of March, April, May. It is not classed in 394.26972 Holidays of Mexico because the class-elsewhere note under 394.269 says to class specific holidays in 394.261-394.267.
Saturday, May 6, is Free Comic Book Day, celebrated annually in independent comic book specialty stores. A locator is available for participating stores. Most of the 28 free comics that will be given away are classed in 741.5973 United States comic books (including manga by American creators), but not all, e.g., one by French cartoonists Philippe Dupuy and Charles Berberian 741.5944 French comic books. Incidentally, these numbers for comic books are unchanged in the new development for 741.5, and you can find more information about the French cartoonists in Lambiek Comiclopedia.