Template:Val/doc

Purpose
This template is used to easily present values in scientific notation, including uncertainty and/or units, as prescribed by Wikipedia's Manual of Style. It wraps the entire result in a nowrap block, so that it never gets broken into separate pieces at the end of a line. (See WP:NBSP for more information on the usage of non-breaking spaces.)

Arguments
There are four ways this template can be used: They all take roughly the same arguments
 * - for displaying values without uncertainty/significance.
 * - for displaying values with uncertainty like so $1,234$.
 * - for displaying values with uncertainty like so $1,234$.
 * - for displaying values with significance like so $1,234$.

See val/test for a list of examples of the correct output of val and the errors it may return when incorrectly used.

Errors
There is strict checking on the validity of arguments; any incorrect use will result in an error, which is displayed using FormattingError. Pages that contain incorrect use of this template will show up on Category:Pages with incorrect formatting templates use.

Format convention
As mentioned before, val should produce formatting compliant with Wikipedia's Manual of Style. It currently produces formatting compliant with the U.S. Government Printing Office Style Manual, in rules 12.9e and 12.14, which requires that the decimal separator be a full stop; i.e. “decimal point” (.), requires comma-delimiting to the left of the decimal point for numbers with four or more digits to the left (values of $e$ or more), and also requires space-delimiting to the right of the decimal point for numbers containing five or more digits to the right (e.g., $123.24$ and $123.24$ and $123.23$).

Note that if is used on numbers simultaneously comprising four or more digits to the left of the decimal point and five or more digits to the right, the resultant expression will delimited with commas left and spaces (actually non-selectable, non-breaking, narrow gaps) right (see below).

Examples



 * colspan=3|Uncertainty/significance
 * colspan=3|Exponents/units
 * colspan=3|Prefix/suffix
 * colspan=3|Numerator/Denominator
 * }
 * colspan=3|Uncertainty/significance
 * colspan=3|Exponents/units
 * colspan=3|Prefix/suffix
 * colspan=3|Numerator/Denominator
 * }
 * colspan=3|Exponents/units
 * colspan=3|Prefix/suffix
 * colspan=3|Numerator/Denominator
 * }
 * colspan=3|Exponents/units
 * colspan=3|Prefix/suffix
 * colspan=3|Numerator/Denominator
 * }
 * colspan=3|Prefix/suffix
 * colspan=3|Numerator/Denominator
 * }
 * colspan=3|Prefix/suffix
 * colspan=3|Numerator/Denominator
 * }
 * colspan=3|Prefix/suffix
 * colspan=3|Numerator/Denominator
 * }
 * colspan=3|Prefix/suffix
 * colspan=3|Numerator/Denominator
 * }
 * colspan=3|Prefix/suffix
 * colspan=3|Numerator/Denominator
 * }
 * colspan=3|Prefix/suffix
 * colspan=3|Numerator/Denominator
 * }
 * colspan=3|Numerator/Denominator
 * }
 * }
 * }
 * }


 * More examples See the testcases at Val/test.

Performance impact
For most uses, in the text of articles, Template:Val will not restrict performance, but when used inside the wikitext markup of large templates, there are some restrictions. When displaying integer amounts, Template:Val has an internal expansion depth of 15 levels, but for numbers with decimal portions, it uses 22 levels, or more.

How to add units
The unit you will add is required to have a link version and a non-link version for stylistic reasons (including the ability of editors to avoid overlinking). The link version will be added to Val/unitswithlink to process the  and   parameters. The non-link version might need to be added to Val/units to process the  and   parameter; it depends on whether or not the unit needs markup, or if the characters users will give to the   or   parameter are different than what is displayed, or if "technical reasons" are discovered. (See below.)

Note these points before adding units:
 * For composite units you should probably link the whole, not individual units. For example the line you add would say  linking to Velocity, not .  List of common physics notations has many examples of composite units that have there own page.
 * The val user can compose their own divisor unit from an existing unit, writing to render there own "$123.23$" with two links:    to Meter and   to Second.
 * The val user can compose their own multiplier units by using the  parameter to prepend a string.  For example, to prepend "$123.23$", they could write, rendering "$123.23$". These cannot be linked.

The technique involves activating "Show changes" to catch unintended changes that are otherwise difficult to detect in any of the many pages using val that would be affected. The last step is an important to the manual of style for dates and numbers.
 * 1) Edit Val/unitswithlink/test.  The LHS of the "=" sign is what val users will give to the   (or  ) parameter. Activate "Show preview".  This will run your test data through val, which would be similar to running val itself in a sandbox. Prove the intended link and markup here because you will not be able to show a preview in the next steps. Copy what you will be adding to the wiki with the next steps. Save the page to serve as a "current list".
 * 2) Edit Val/unitswithlink.  Paste the identical line proven in step 1.  Sort order is not important. Show changes, and then save.
 * 3) If the unit will display differently from what is typed into , edit Val/units. Paste the identical line, and remove any links from the RHS of the "=" sign, being careful to leave any rendering work. Show changes, and then save.
 * 4) Important. Run   and   in a sandbox and verify that your unit has an identical appearance in both cases. Edit Val/units to make any corrections. (The discrepancy occured for technical reasons.)

FAQ and comments

 * Q: Why should I use val?
 * A1: Val formats numbers:
 * inserts commas into large numbers and spaces between decimal digits
 * handles uncertainties in measurements and significant digits, providing a ± character, etc.
 * handles exponents of 10 and scientific notation
 * replaces "-" (hyphen) with a "&minus;" (minus sign)
 * A2: It preserves spacing:
 * It makes sure the value does not wrap at the end of a line, so that it can always be read as a single value on one line in the text.
 * It spaces the various parts of the value where they should be
 * A3: It automates the markup for, and a link to a displayed unit.
 * A4: Val helps make Wikipedia more consistent. It adheres to the Wikipedia Manual of Style for numbers. Updates to the Wikipedia Manual of Style for numbers can be applied to this template, and result in automatic modification on values that use val. All this makes sure all values on all pages have the same look and feel because they will all use the same spacing, font size, positioning, etc, and makes updating and checking by the bots easier because they can recognize a value for what it is.


 * Q: Why not use ?
 * A: For the same reasons HTML might be preferred over :
 * Because the font in math tags differs both in face and size from the prose, which can disturb the layout of a page when used inline with the prose.
 * You cannot cut and paste a bitmap image rendered by the Latex.
 * Images are slower to load and use more bandwidth, which is especially bad for the mobile version of Wikipedia.
 * does not automatically adhere to the Wikipedia Manual of Style for numbers.


 * Q: Are there any known issues with val?
 * A1: Because numbers can only be stored with a limited precision by Wikipedia servers, val cannot handle very large numbers, such as 123456789123456789. This is reported using a FormattingError, so it should be easy to spot. Since there is very limited use for such large numbers, there is no fix planned for this.
 * A2: This template has been in full use on many pages for quite some time without major problems or breaking changes. Technically, there is no good reason not to try val.


 * Q: How should I use val?
 * A1: Val probably already has your unit on its current list. If not, then your unit can be added.
 * A2: To avoid over linking switch from the ul= to the u= parameter of the given unit.