ASS values
Following Lua tables+elements/fields are describing the content of input ASS file (parsed with io.load_ass function).
They're immediately available at beginning of code execution.

meta	Script meta data table
.comment	Script comments string
.title	Script title string
.script_type	Script version string
.wrap_style	Line wrap style number
.width	Video width number
.height	Video height number
.scaled_border_and_shadow	Border/shadow scaled by different real video and script resolution? boolean
.ratio	Video ratio (seems to change nothing) number
.zoom	Video zoom (just for editing) number
.position	Current video frame for playback (just for editing) number
.last_style	Last style storaged string
.audio	Loaded audio file string
.video	Loaded video file string

styles	Styles table
[i]	Single style table
.name	Style name string
.fontname	Style font name string
.fontsize	Style font size number
.color1	Style fill color string
.alpha1	Style fill alpha string
.color2	Style karaoke color string
.alpha2	Style karaoke alpha string
.color3	Style outline color string
.alpha3	Style outline alpha string
.color4	Style shadow color string
.alpha4	Style shadow alpha string
.bold	Style font bold? boolean
.italic	Style font italic? boolean
.underline	Style font underlined? boolean
.strikeout	Style font strikeouted? boolean
.scale_x	Style horizontal scale number
.scale_y	Style vertical scale number
.spacing	Style text spacing number
.angle	Style text z rotation number
.borderstyle	Style border type -> opaque box (else rounded border)? boolean
.outline	Style font border size number
.shadow	Style font shadow offset position (down-right) number
.alignment	Style video alignment number
.margin_l	Style position offset from left video side number
.margin_r	Style position offset from right video side number
.margin_v	Style position offset from video top and bottom number
.encoding	Style font encoding number

lines	Dialog lines table
[i]	Single dialog line table
.comment	Line is a comment? boolean
.layer	Line layer number
.start_time	Line start time (in milliseconds) number
.end_time	Line end time (in milliseconds) number
.mid_time	Line mid time (in milliseconds) number
.duration	Line duration (in milliseconds) number
.infade	Line infade duration (in milliseconds; first line = 1000.1) number
.outfade	Line outfade duration (in milliseconds, last line = 1000.1) number
.style	Line style name string
.styleref	Line style table table
.actor	Line actor string
.margin_l	Line position offset from left video side number
.margin_r	Line position offset from right video side number
.margin_v	Line position offset from video top and bottom number
.effect	Line effect description string
.k_text	Line raw text string
.text	Line stripped text string
.i	Line index number
.width	Line text width number
.height	Line text height number
.ascent	Line font ascent number
.descent	Line font descent number
.intlead	Line font internal lead number
.extlead	Line font external lead number
.x	Line text position horizontal (depends on alignment) number
.y	Line text position vertical (depends on alignment) number
.left	Line text position left number
.center	Line text position center number
.right	Line text position right number
.top	Line text position top number
.middle	Line text position middle number
.bottom	Line text position bottom number
.syls	Line sylables table
[i]	Single line sylable table
.i	Sylable index number
.word_i	Sylable word index number
.start_time	Sylable start time (in milliseconds) number
.end_time	Sylable end time (in milliseconds) number
.mid_time	Sylable mid time (in milliseconds) number
.duration	Sylable duration (in milliseconds) number
.text	Sylable text string
.inline_fx	Sylable inline effect (marked as \\-EFFECT in karaoke-time) string
.prespace	Sylable free space before text number
.postspace	Sylable free space after text number
.width	Sylable text width number
.height	Sylable text height number
.ascent	Sylable font ascent number
.descent	Sylable font descent number
.intlead	Sylable font internal lead number
.extlead	Sylable font external lead number
.x	Sylable text position horizontal (depends on alignment) number
.y	Sylable text position vertical (depends on alignment) number
.left	Sylable text position left number
.center	Sylable text position center number
.right	Sylable text position right number
.top	Sylable text position top number
.middle	Sylable text position middle number
.bottom	Sylable text position bottom number
.chars	Line characters table
[i]	Single line character table
.i	Character index number
.syl_i	Character sylable index number
.word_i	Character word index number
.start_time	Character start time (in milliseconds) number
.end_time	Character end time (in milliseconds) number
.mid_time	Character mid time (in milliseconds) number
.duration	Character duration (in milliseconds) number
.text	Character text string
.width	Character text width number
.height	Character text height number
.ascent	Character font ascent number
.descent	Character font descent number
.intlead	Character font internal lead number
.extlead	Character font external lead number
.x	Character text position horizontal (depends on alignment) number
.y	Character text position vertical (depends on alignment) number
.left	Character text position left number
.center	Character text position center number
.right	Character text position right number
.top	Character text position top number
.middle	Character text position middle number
.bottom	Character text position bottom number
.words	Line words table
[i]	Single line word table
.i	Word index number
.start_time	Word start time (in milliseconds) number
.end_time	Word end time (in milliseconds) number
.mid_time	Word mid time (in milliseconds) number
.duration	Word duration (in milliseconds) number
.text	Word text string
.prespace	Word free space before text number
.postspace	Word free space after text number
.width	Word text width number
.height	Word text height number
.ascent	Word font ascent number
.descent	Word font descent number
.intlead	Word font internal lead number
.extlead	Word font external lead number
.x	Word text position horizontal (depends on alignment) number
.y	Word text position vertical (depends on alignment) number
.left	Word text position left number
.center	Word text position center number
.right	Word text position right number
.top	Word text position top number
.middle	Word text position middle number
.bottom	Word text position bottom number

Additional information