is there a place where there is line by line instructions for filling out the long stay immigration forms? some of the answers are obvious and some are not so obvious. i'm looking for the USA version

This is taken from the London Embassy website, relating to Non-immigrant Visas (including Type O):

'Multiple Entries Visa will be valid for 1 year from the date of issue. You must enter Thailand within the validity of visa. However, the permitted length of stay is up to 1 year from the date of your arrival in Thailand. Please carefully note the immigration stamp in your passport to make sure that you do not overstay your visa.'

This seems to say that the multi-entry visa is stamped allowing a visit length of one year. I'm a little confused as previous remarks in the group have implied that the length of stay is only 90 days. Can anyone clarify this?