Known limitations¶

Behaviour of TriasDev.Tabular that is wrong at the edges, or looser than it reads, and has not been changed yet — each with what would make it matter, so you can tell whether it affects your files. None of them loses or silently alters data in files an ordinary producer writes; where one could, it says so and links the issue that tracks it.

Found a case that belongs here, or one of these that bites you? Open an issue; a real file that hits an entry is the best reason to fix it.

Correctness at the edges¶

A stray quote closed at a field boundary within less than a record joins two lines¶

A quote that opens a field and is closed on a later line by a quote followed by a delimiter or a line ending is read as one field spanning lines, as RFC 4180 says — unless the field has by then swallowed a whole record's worth of delimiters, which marks it as a stray quote (#20, #10). A stray quote that happens to be closed at a field boundary before that point keeps the two lines joined: nothing in the text tells it from a genuine multi-line value. In tables narrower than five columns the delimiter test is off, and only the 100-line bound catches a stray quote.

Matters when a producer writes lone quotes into fields often enough for two of them to meet at a field boundary within one record. Neither the real-world nor the synthetic 5M-row fixture has such a case.

A `numFmt` inside `<dxfs>` can overwrite a cell format¶

Number formats are collected from anywhere in styles.xml. Differential formats — used by conditional formatting — live in <dxfs> and carry their own ids. One colliding with a custom id (164 and up) flips a column between numbers and dates.

Matters when a file uses conditional formatting and custom number formats, and the ids collide. Fix by tracking whether the reader is inside <numFmts>, as it already does for <cellXfs>.

Number formats the reader does not know are dates¶

IsBuiltInDateFormat accepts 14–22 and 45–47. The specification also reserves 27–36 and 50–58 for dates in East Asian locales. A cell using one reads as a number.

`applyNumberFormat="0"` is ignored¶

The attribute says the format is not applied. Honouring it would change whether a styled cell is read as a date.

`t="b"` accepts only `"1"`, and `date1904` only `"1"` and `"true"`¶

The schema type is xsd:boolean, which also permits "true"/"false" and "0". A writer using the long spelling produces a boolean read as false, or a 1904 workbook read as 1900 — the latter is a four-year error.

Relationship targets are not percent-decoded¶

Parts are found through the package relationships, and targets are resolved against their folder, ../ included. A target that percent-encodes its name (sheet%201.xml) is not decoded, so it is looked up literally and not found. No producer seen writes one.

A whitespace-only string is dropped one way and kept the other¶

A shared string of spaces without xml:space="preserve" is dropped, because that path reads with XmlReader and IgnoreWhitespace. The same content written inline is kept, because the scanner has no such notion. Same value, two answers, depending only on how the writer chose to store it.

Rows that repeat a row number are read as successive rows¶

A worksheet that writes every cell in a <row> of its own, all carrying r="1", is read as that many rows, each with one cell; LibreOffice joins them into one. Row numbers here never go backwards or repeat, so a message never points at a row twice. Seen once, in one writer's output. Matters if a producer that writes this way turns up among real files.

An OpenDocument error cell carries the writer's text, not an Excel code¶

LibreOffice writes a formula that failed with its own wording — Err:502 where Excel would say #VALUE! — and recalculates on saving, so a workbook converted to .ods can hold different errors, and different values in volatile or unsupported formulas, than the original. Read as written; a caller comparing the two formats sees the writer's differences, not the reader's.

Flat OpenDocument (`.fods`) and Excel 2003 XML are not read¶

Both are a spreadsheet as one plain XML document, without the zip. A file that opens with an XML declaration is refused as unsupported rather than read as csv. Matters if anyone sends one.

Chartsheets and hidden sheets are indistinguishable from ordinary ones¶

SheetInfo carries a name and an index. A caller cannot tell a hidden sheet, or a chartsheet with no cells, from a sheet the user meant.

Contracts looser than they read¶

A number written in exponential notation is read as text¶

Both the profiler and the extractor parse decimals with NumberStyles.Number, which does not include AllowExponent. Measured against .NET rather than inferred:

value	`NumberStyles.Number`	`NumberStyles.Float`
`5.4176e-03`	rejected	0.0054176
`1E+5`	rejected	100000
`-2.5e2`	rejected	-250

The consequence is worse than a refused row, because it happens at analysis too: a column of such values is profiled as text, so a decimal is never proposed for it, and a mapping to a decimal field then fails every row with value.type-mismatch.

Found on a real export — a column carried 5.4176e-03 — so this is not hypothetical. NumberStyles.Float would fix both places, and the reason it has not been changed yet is not the one this entry used to give. Float does not include AllowThousands, which Number does — measured, 1,234.56 reads under Number and is rejected under Float. Losing grouped numbers in a library whose stated subject is telling 1.234,56 from 1,234.56 would be a worse defect than the one being fixed, so the change is Number | AllowExponent rather than Float, and it has to land in the profiler and the extractor together or a column will be proposed as a decimal the extractor refuses.

Matters when any file carries scientific notation — scientific instruments, financial exports and anything that has been through a naive double.ToString() all do.

A date must carry two separators, so `15 Jan 2023` is text¶

DateReading.LooksLikeOne requires two of -, /, ., or a colon, before a parse is attempted. That is what refuses a decimal (1.5 reads as the fifth of January under en-US) and a day-and-month (3/15 takes the current year), and the price is a date written with spaces and a month name.

A genuine 0001-01-01 is refused for the neighbouring reason: year one is the marker that the text named no year.

Matters when a customer exports dates in a long form. The fix is a parse against the culture's year-bearing patterns rather than a shape test, which is more code than the case has so far earned.

Dates cannot carry a range¶

MinValue/MaxValue compare numbers, so a range on a date field is refused by the validator (mapping.constraint-type-mismatch) rather than silently judged against zero, as it once was. Date ranges — the obvious second use — cannot be expressed yet.

Matters as soon as a caller wants one. Fix with a date-typed range constraint.

`CsvCursor.MoveToSheet` does not rewind¶

The interface documents "positions before its first row"; the csv implementation returns index == 0 and stays where it is. Analysing and then extracting through one cursor instance reads a csv from wherever it stopped. A csv inside an archive does rewind: the archive reopens its file.

Moving to a sheet cannot be cancelled¶

ITabularCursor.MoveToSheet takes no token. For an OpenDocument spreadsheet it reads forward through the content part to the sheet, and for a workbook inside an archive it copies the workbook into memory, so a move can take seconds on a large file. The first move, made while the cursor is opened, does observe the opening's token. Matters if an import must stop within a second while it changes sheets; fixing it means a token on the interface, in a minor release.

`IsBlank` ignores the binding's empty-equivalents¶

A row whose every mapped cell holds k.A. is not skipped. It is counted as produced and handed over as a valid row of entirely absent values.

`RowError.RawValue` is the trimmed value¶

The spec says the value "as it appeared in the file". Trimming is on by default, so a value failing a length rule because of its spaces is reported without them, pointing at something that looks right.

`ValidateOnly` returns a full-length span of absent values¶

Indistinguishable from a row where every field was legitimately empty.

`MappedValue` accessors throw, and say nothing about it¶

Date on a decimal value throws; Integer on a large one throws. RawCell documents exactly this hazard for the identical design. MappedValue.Absent also reports Type == Text, so an absent value is indistinguishable from an absent text value.

`MappedValue.FromDate` loses the time of day in `Text`¶

Every length, pattern and allowed-value constraint sees Text, so a datetime is validated against a date-only string while Date still carries the ticks.

`CsvDialect` lets a caller claim a value was detected¶

EncodingSource and DelimiterSource are required on a record a caller constructs to override detection. The provenance exists so a UI can tell a fact from a guess; a hand-built dialect can lie about it.

A byte order mark overrides a caller-specified encoding¶

StreamReader is constructed with detectEncodingFromByteOrderMarks: true alongside the chosen encoding.

The dialect override is all or nothing¶

A caller who knows only the delimiter must also supply the encoding, losing detection for it. There is no per-property override, no line-ending member, and the quote character is hard-coded with no provenance.

The package ceiling counts bytes off the wire, not memory¶

MaxUncompressedBytes sums the entries' declared sizes. Text decoded to UTF-16 doubles, and a buffer that grows to hold a token peaks at three times its content. The scanner buffer and the csv field have their own ceilings, which carry most of this weight, but the package ceiling by itself is not the bound it appears to be.

A zip entry that understates its size is read short, without an error¶

The runtime's zip reader stops an entry at the size its headers declare and does not check the checksum, so a crafted archive — or a buggy writer — that declares 10 bytes for a csv of a hundred thousand rows yields its first rows as a plausible, shorter table. Workbook parts are read the same way. An upload cut off in transit is not this case: it loses the directory at the end and is refused as damaged. Catching it needs a CRC-32 over every byte read, which the base class library offers on no x86 processor, and a table-driven one costs about half a second on the 572 MB csv. Matters if files come from a writer that gets sizes wrong.

A pattern constraint is bounded per value, not per run¶

The match timeout is 100 ms. A pattern using a lookaround falls back to the backtracking engine, and a million rows at 100 ms each is a run measured in hours. Compilation is not bounded at all: a pattern with large counted quantifiers costs time and memory before any value is seen.

Matters when patterns become admin-authored or config-driven rather than domain-authored.

Per-column allowances multiply by the column count¶

Each column keeps ten first values, sixty-four frequency keys and up to a hundred and twenty located outliers, each an unbounded string. The column count is now bounded by the format's last column, so the product is bounded — but it is 16,384 times those allowances.

A workbook's own strings have no length ceiling¶

Sheet names, relationship targets and number-format codes are taken straight from the package with a ceiling on how many there may be and none on how long each may be. Measured: 4,096 sheets — exactly the permitted number — with 400,000-character names is a 1.65 MB upload that retains 3,125 MB for the cursor's whole life.

This is the third appearance of one mistake: a ceiling on the number of things rather than on their size. It was fixed for the shared string table, which has both, and left standing on its three siblings.

Matters when somebody sends a file built to do this. An ordinary export cannot reach it.

A sheet whose part is missing aborts the analysis¶

MoveToSheet throws rather than returning false, so a workbook declaring a sheet whose part is absent fails the whole pass instead of skipping it.

Deliberate choices¶

Decided, not deferred — listed so they are not mistaken for gaps.

Synchronous throughout. Parsing is processor work over a buffered stream, and a row cannot be a ReadOnlySpan<T> and be awaited at once. See the remarks on ITabularCursor.
No comment syntax in csv. The format does not define one. Add it if the files we receive use it.
The header is the first row. No heuristic looks elsewhere; MappingPlan.HeaderRowIndex is where a user says otherwise.
"C" Road is repaired without a diagnostic. The repair is lossy, and unlike an unterminated quote it is not counted. Whether it should be is a judgement, not an oversight.