Use this method carefully. It can override a property that is coming from another class if multiple classes are used at the same time. Take a look at the next HTML and CSS codes:

<div class="test1 test2">
    This is an example
</div>    

.test1 {
    background: #666;
    color: #FFF;
    padding: 20px;
}

.test2 {
    padding-right: 10px;
}

Using the combined method, the generated code will be the next one:

.test1 {
    background: #666;
    color: #FFF;
    padding: 20px;
}

[dir="ltr"] .test2 {
    padding-right: 10px;
}

[dir="rtl"] .test2 {
    padding-left: 10px;
}

So, the div will have a padding of 20px 10px 20px 20px in LTR and 20px 20px 20px 10px in RTL.

However, using the override method the generated code will be the next one:

.test1 {
    background: #666;
    color: #FFF;
    padding: 20px;
}

.test2 {
    padding-right: 10px;
}

[dir="rtl"] .test2 {
    padding-right: 0;
    padding-left: 10px;
}

Now the div has a padding of 20px 10px 20px 20px in LTR and 20px 0 20px 10px in RTL, because the override of the class test2 doesn't take into account that this class could be used with test1 having the same properties. The solution, in this case, is to provide the property that has been inherited:

.test1 {
    background: #666;
    color: #FFF;
    padding: 20px;
}

.test2 {
    padding-left: 20px;
    padding-right: 10px;
}

So, the generated code will be:

.test1 {
    background: #666;
    color: #FFF;
    padding: 20px;
}

.test2 {
    padding-left: 20px;
    padding-right: 10px;
}

[dir="rtl"] .test2 {
    padding-right: 20px;
    padding-left: 10px;
}

The mode option has been explained in the Output using the combined mode and Output using the override mode sections. To avoid using magic strings, the package exposes an object with these values, but it is possible to use strings values:

import postcss from 'postcss';
import postcssRTLCSS from 'postcss-rtlcss';
import Options from 'postcss-rtlcss/options';

const input = '... css code ...';
const optionsCombined = { mode: Options.Mode.combined }; // This is the default value
const optionsOverride = { mode: Options.Mode.override };

const outputCombined = postcss([
    postcssRTLCSS(optionsCombined)
]).process(input);

const outputOverride = postcss([
    postcssRTLCSS(optionsOverride)
]).process(input);

These two options manage the prefix strings for each direction. They can be strings or arrays of strings:

input

.test1, .test2 {
    left: 10px;
}

.test3,
.test4 {
    text-align: left;
}

Using strings

const options = {
    ltrPrefix: '.ltr',
    rtlPrefix: '.rtl'
};

output

.ltr .test1, .ltr .test2 {
    left: 10px;
}

.rtl .test1, .rtl .test2 {
    right: 10px;
}

.ltr .test3,
.ltr .test4 {
    text-align: left;
}

.rtl .test3,
.rtl .test4 {
    text-align: right;
}

Using arrays of strings

const options = {
    ltrPrefix: ['[dir="ltr"]', '.ltr'],
    rtlPrefix: ['[dir="rtl"]', '.rtl']
};

output

[dir="ltr"] .test1, .ltr .test1, [dir="ltr"] .test2, .ltr .test2 {
    left: 10px;
}

[dir="rtl"] .test1, .rtl .test1, [dir="rtl"] .test2, .rtl .test2 {
    right: 10px;
}

[dir="ltr"] .test3,
.ltr .test3,
[dir="ltr"] .test4,
.ltr .test4 {
    text-align: left;
}

[dir="rtl"] .test3,
.rtl .test3,
[dir="rtl"] .test4,
.rtl .test4 {
    text-align: right;
}

This prefix will be used in some specific cases in which a ltr or rtl rule will override declarations located in the main rule due to specificity. Consider the next example using the option processUrls as true:

.test1 {
    background: url('icons/ltr/arrow.png');
    background-size: 10px 20px;
    width: 10px;
}

The generated CSS would be:

.test1 {
    background-size: 10px 20px;
    width: 10px;
}

[dir="ltr"] .test1 {
    background: url('icons/ltr/arrow.png');
}

[dir="rtl"] .test1 {
    background: url('icons/rtl/arrow.png');
}

In the previous case, the background-size property has been overridden by the background one. Even if we change the order of the rules, the last ones have a higher specificity, so they will rule over the first one.

To solve this, another rule will be created at the end using the bothPrefix parameter:

.test1 {
    width: 10px;
}

[dir="ltr"] .test1 {
    background: url('icons/ltr/arrow.png');
}

[dir="rtl"] .test1 {
    background: url('icons/rtl/arrow.png');
}

[dir] {
    background-size: 10px 20px;
}

And no matter the direction, the background-size property is respected.

This option will add the boxPrefix option to those declarations that can be flipped, no matter if they are not overridden in the same rule. This avoids them being overridden by specificity of other flipped declarations contained in other rules. For example, let's consider that we have a div element with the next rules:

<div class="test1 test2">
    This is an example
</div> 

.test1 {
    color: #FFF;
    padding: 4px 10px 4px 20px;
    width: 100%;
}

.test2 {
    padding: 0;
}

The expecting result is that the padding of the element becomes 0 as it has been reset by test2. With safeBothPrefix in false, the generated CSS will be:

.test1 {
    color: #FFF;
    width: 100%;
}

[dir="ltr"] .test1 {
    padding: 4px 10px 4px 20px;
}

[dir="rtl"] .test1 {
    padding: 4px 20px 4px 10px;
}

.test2 {
    padding: 0;
}

The result is that the padding properties of test1 have more specificity than the same property in tes2, so it is not reset if both rules are applied at the same time. Let's check the result if safeBothPrefix is true:

.test1 {
    color: #FFF;
    width: 100%;
}

[dir="ltr"] .test1 {
    padding: 4px 10px 4px 20px;
}

[dir="rtl"] .test1 {
    padding: 4px 20px 4px 10px;
}

[dir] .test2 {
    padding: 0;
}

As test2 has the same level of specificity as test1, now the result is that the padding is reset if both rules are used at the same time.

This option is to ignore the rules that have been prefixed with one of the prefixes contained in ltrPrefix, rtlPrefix, or bothPrefix:

input

[dir="ltr"] test {
    left: 10px;
}

[dir="rtl"] test {
    right: 10px;
}

ignorePrefixedRules true

const options = { ignorePrefixedRules: true }; // This is the default value

output

[dir="ltr"] test {
    left: 10px;
}

[dir="rtl"] test {
    right: 10px;
}

ignorePrefixedRules false

const options = { ignorePrefixedRules: false };

output

[dir="ltr"] [dir="ltr"] test {
    left: 10px;
}

[dir="rtl"] [dir="ltr"] test {
    right: 10px;
}

[dir="ltr"] [dir="rtl"] test {
    right: 10px;
}

[dir="rtl"] [dir="rtl"] test {
    left: 10px;
}

This option manages if the conversion will be from LTR to RTL or vice versa.

input

.test1, .test2 {
    left: 10px;
}

Using Source.ltr in combined mode

import Options from 'postcss-rtlcss/options';

const options = {
    mode: Options.Mode.combined,
    source: Options.Source.ltr // This is the default value
};

output

[dir="ltr"] .test1, [dir="ltr"] .test2 {
    left: 10px;
}

[dir="rtl"] .test1, [dir="rtl"] .test2 {
    right: 10px;
}

Using Source.rtl in override mode

import Options from 'postcss-rtlcss/options';

const options = {
    mode: Options.Mode.override,
    source: Options.Source.rtl
};

output

.test1, .test2 {
    left: 10px;
}

[dir="ltr"] .test1, [dir="ltr"] .test2 {
    left: auto;
    right: 10px;
}

This options manages if the strings of the URLs should be flipped taken into account the string map:

input

.test1, .test2 {
    background-image: url("./folder/subfolder/icons/ltr/chevron-left.png");
    left: 10px;
}

processUrls false

const options = { processUrls: false }; // This is the default value

output

.test1, .test2 {
    background-image: url("./folder/subfolder/icons/ltr/chevron-left.png");
}

[dir="ltr"] .test1, [dir="ltr"] .test2 {
    left: 10px;
}

[dir="rtl"] .test1, [dir="rtl"] .test2 {
    right: 10px;
}

processUrls true

const options = { processUrls: true };

output

[dir="ltr"] .test1, [dir="ltr"] .test2 {
    background-image: url("./folder/subfolder/icons/ltr/chevron-left.png");
    left: 10px;
}

[dir="rtl"] .test1, [dir="rtl"] .test2 {
    background-image: url("./folder/subfolder/icons/rtl/chevron-right.png");
    right: 10px;
}

This option manages if the @keyframes animation rules should be flipped:

input

.test1 {
    animation: 5s flip 1s ease-in-out;
    color: #FFF;
}

@keyframes flip {
    from {
        transform: translateX(100px);
    }
    to {
        transform: translateX(0);
    }
}

processKeyFrames false

const options = { processKeyFrames: false }; // This is the default value

output

.test1 {
    animation: 5s flip 1s ease-in-out;
    color: #FFF;
}

@keyframes flip {
    from {
        transform: translateX(100px);
    }
    to {
        transform: translateX(0);
    }
}

processKeyFrames true

const options = { processKeyFrames: true };

output

.test1 {
    color: #FFF;
}

[dir="ltr"] .test1 {
    animation: 5s flip-ltr 1s ease-in-out;
}

[dir="rtl"] .test1 {
    animation: 5s flip-rtl 1s ease-in-out;
}

@keyframes flip-ltr {
    from {
        transform: translateX(100px);
    }
    to {
        transform: translateX(0);
    }
}

@keyframes flip-rtl {
    from {
        transform: translateX(-100px);
    }
    to {
        transform: translateX(0);
    }
}

This options manages if the agent-defined environment variables should be flipped:

input

body {
    padding:
        env(safe-area-inset-top, 10px)
        env(safe-area-inset-right, 20px)
        env(safe-area-inset-bottom, 30px)
        env(safe-area-inset-left, 40px)
    ;
}

.test1 {
    margin-right: env(safe-area-inset-right, 10px);
    margin-left: env(safe-area-inset-left, 20px);
}

processEnv true

const options = { processEnv: true }; // This is the default value

output

[dir=\\"ltr\\"] body {
    padding:
        env(safe-area-inset-top, 10px)
        env(safe-area-inset-right, 20px)
        env(safe-area-inset-bottom, 30px)
        env(safe-area-inset-left, 40px)
    ;
}

[dir=\\"rtl\\"] body {
    padding:
        env(safe-area-inset-top, 10px)
        env(safe-area-inset-right, 40px)
        env(safe-area-inset-bottom, 30px)
        env(safe-area-inset-left, 20px);
}

[dir=\\"ltr\\"] .test1 {
    margin-right: env(safe-area-inset-right, 10px);
    margin-left: env(safe-area-inset-left, 20px);
}

[dir=\\"rtl\\"] .test1 {
    margin-left: env(safe-area-inset-left, 10px);
    margin-right: env(safe-area-inset-right, 20px);
}

processEnv false

const options = { processEnv: false };

output

[dir=\\"ltr\\"] body {
    padding:
        env(safe-area-inset-top, 10px)
        env(safe-area-inset-right, 20px)
        env(safe-area-inset-bottom, 30px)
        env(safe-area-inset-left, 40px)
    ;
}

[dir=\\"rtl\\"] body {
    padding:
        env(safe-area-inset-top, 10px)
        env(safe-area-inset-left, 40px)
        env(safe-area-inset-bottom, 30px)
        env(safe-area-inset-right, 20px);
}

[dir=\\"ltr\\"] .test1 {
    margin-right: env(safe-area-inset-right, 10px);
    margin-left: env(safe-area-inset-left, 20px);
}

[dir=\\"rtl\\"] .test1 {
    margin-left: env(safe-area-inset-right, 10px);
    margin-right: env(safe-area-inset-left, 20px);
}

When this option is enabled, it flips background-position, background-position-x and transform-origin properties if they are expressed in length units using calc:

input

.test {
    background-image: url("./folder/subfolder/icons/ltr/chevron-left.png");
    background-position-x: 5px;
    left: 10px;
    transform-origin: 10px 20px;
    transform: scale(0.5, 0.5);
}

useCalc false

const options = { useCalc: false }; // This is the default value

output

.test {
    background-image: url("./folder/subfolder/icons/ltr/chevron-left.png");
    background-position-x: 5px;
    transform-origin: 10px 20px;
    transform: scale(0.5, 0.5);
}

[dir="ltr"] .test {
    left: 10px;
}

[dir="rtl"] .test {
    right: 10px;
}

useCalc true

const options = { useCalc: true };

output

.test {
    background-image: url("./folder/subfolder/icons/ltr/chevron-left.png");
    transform: scale(0.5, 0.5);
}

[dir="ltr"] .test {
    background-position-x: 5px;
    left: 10px;
    transform-origin: 10px 20px;
}

[dir="rtl"] .test {
    background-position-x: calc(100% - 5px);
    right: 10px;
    transform-origin: calc(100% - 10px) 20px;
}

An array of strings maps that will be used to make the replacements of the URLs and rules selectors names. The name parameter is optional, but if you want to override any of the default string maps, just add your own using the same name.

// This is the default string map object
const options = {
    stringMap: [
        {
            name: 'left-right',
            search : ['left', 'Left', 'LEFT'],
            replace : ['right', 'Right', 'RIGHT']
        },
        {
            name: 'ltr-rtl',
            search  : ['ltr', 'Ltr', 'LTR'],
            replace : ['rtl', 'Rtl', 'RTL'],
        }
    ]
};

Flip or not the selectors names of the rules without directional properties using the stringMap.

input

.test1-ltr {
    color: #FFF;
}

.test2-left::before {
    content: "\f007";
}

.test2-right::before {
    content: "\f010";
}

Using Autorename.flexible

import Options from 'postcss-rtlcss/options';

const options = {
    autoRename: Options.Autorename.flexible
};

output

.test1-rtl {
    color: #FFF;
}

.test2-right::before {
    content: "\f007";
}

.test2-left::before {
    content: "\f010";
}

Using Autorename.strict

import Options from 'postcss-rtlcss/options';

const options = {
    autoRename: Options.Autorename.strict
};

output

/* This selector will not be flipped because it doesn't have a counterpart */
.test1-ltr {
    color: #FFF;
}

.test2-right::before {
    content: "\f007";
}

.test2-left::before {
    content: "\f010";
}

When autoRename is enabled and greedy is true, the strings replacements will not take into account word boundaries.

input

.test1-ltr {
    color: #FFF;
}

.test2ltr {
    width: 100%;
}

greedy false

import Options from 'postcss-rtlcss/options';

const options = {
    autoRename: Options.Autorename.flexible,
    greedy: false // This is the default value
};

output

.test1-rtl {
    color: #FFF;
}

.test2ltr {
    width: 100%;
}

greedy true

import Options from 'postcss-rtlcss/options';

const options = {
    autoRename: Options.Autorename.flexible,
    greedy: true
};

output

.test1-rtl {
    color: #FFF;
}

.test2rtl {
    width: 100%;
}

This property consists of a string map to treat some declarations as others, very useful to flip the values of CSS variables.

Note: This property is not available in the legacy version of the package

input

:root {
    --my-padding: 1rem 1rem 1.5rem 1.5rem;
}

.test {
    padding: var(--my-padding);
}

No aliases string map (default)

output

:root {
    --my-padding: 1rem 1rem 1.5rem 1.5rem;
}

.test {
    padding: var(--my-padding);
}

Set an aliases string map

const options = {
    aliases: {
        '--my-padding': 'padding'
    }
};

output

[dir="ltr"]:root {
    --my-padding: 1rem 1rem 1.5rem 1.5rem;
}

[dir="rtl"]:root {
    --my-padding: 1rem 1.5rem 1.5rem 1rem;
}

.test {
    padding: var(--my-padding);
}

This directive ignores processing of the following rule or declaration. In the next block the whole declaration will be ignored:

input

/*rtl:ignore*/
.test1, .test2 {
    text-align: left;
    left: 10px;
}

output

.test1, .test2 {
    text-align: left;
    left: 10px;
}

In the next block only the left property will be ignored:

input

.test3, .test4 {
    text-align: left;
    /*rtl:ignore*/
    left: 10px;
}

output

.test3, .test4 {
    left: 10px;
}

[dir="ltr"] .test3, [dir="ltr"] .test4 {
    text-align: left;
}

[dir="rtl"] .test3, [dir="rtl"] .test4 {
    text-align: right;
}

These directives should be used together, they will provide the beginning and the end for ignoring rules or declarations.

Note: The directives inserted between these blocks will be ignored and maintained in the final output.

Ignoring multiple rules:

input

/*rtl:begin:ignore*/
.test1, .test2 {
    left: 10px;
    text-align: left;
}

.test3 {
    padding: 1px 2px 3px 4px;
}
/*rtl:end:ignore*/

output

.test1, .test2 {
    left: 10px;
    text-align: left;
}

.test3 {
    padding: 1px 2px 3px 4px;
}

Ignoring multiple declarations:

input

.test1, .test2 {
    left: 10px;
    /*rtl:begin:ignore*/
    margin-left: 4em;
    padding: 1px 2px 3px 4px;
    /*rtl:end:ignore*/
    text-align: left;
}

output

.test1, .test2 {
    margin-left: 4em;
    padding: 1px 2px 3px 4px;
}

[dir="ltr"] .test1, [dir="ltr"] .test2 {
    left: 10px;
    text-align: left;
}

[dir="rtl"] .test1, [dir="rtl"] .test2 {
    right: 10px;
    text-align: right;
}

This directive forces renaming of the following rule or declaration no mattering the value of the properties processUrls or autoRename:

input

/*rtl:rename*/
.test-left {
    width: 100%;
}

.test {
    /*rtl:rename*/
    background-image: url("/icons/icon-left.png");
}

output

.test-right {
    width: 100%
}

[dir="ltr"] .test {
    background-image: url("/icons/icon-left.png");
}

[dir="rtl"] .test {
    background-image: url("/icons/icon-right.png");
}

These directives should be used together, they will provide the beginning and the end for renaming rules or declarations.

input

/*rtl:begin:rename*/
.icon-left {
    content: "\\f40";
}

.icon-right {
    content: "\\f56";
}
/*rtl:end:rename*/

.test {
    /*rtl:begin:rename*/
    background-image: url("/images/background-left.png");
    cursor: url("/images/cursor-ltr.png");
    /*rtl:end:rename*/
}

output

.icon-right {
    content: "\\f40";
}

.icon-left {
    content: "\\f56";
}

[dir="ltr"] .test {
    background-image: url("/images/background-left.png");
    cursor: url("/images/cursor-ltr.png");
}

[dir="rtl"] .test {
    background-image: url("/images/background-right.png");
    cursor: url("/images/cursor-rtl.png");
}

This directive sets the source of a rule or a directive ignoring the value of the source property:

input

/*rtl:source:rtl*/
.test {
    color: #FFF;
    border-left: 1px solid #666;
    padding: 10px 5px 10px 20px;
    text-align: left;
    width: 100%;
}

output

.test {
    color: #FFF;
    width: 100%;
}

[dir="ltr"] .test {
    border-right: 1px solid #666;
    padding: 10px 20px 10px 5px;
    text-align: right;
}

[dir="rtl"] .test {
    border-left: 1px solid #666;
    padding: 10px 5px 10px 20px;
    text-align: left;
}

These directives should be used together, they will provide the beginning and the end of source blocks for rules or declarations:

input

.test {
    color: #FFF;
    border-left: 1px solid #666;
    /*rtl:begin:source:rtl*/
    padding: 10px 5px 10px 20px;
    text-align: left;
    /*rtl:end:source*/
    width: 100%;
}

output

.test {
    color: #FFF;
    width: 100%;
}

[dir="ltr"] .test {
    border-left: 1px solid #666;
    padding: 10px 20px 10px 5px;
    text-align: right;
}

[dir="rtl"] .test {
    border-right: 1px solid #666;
    padding: 10px 5px 10px 20px;
    text-align: left;
}

Parses the CSS parameter and inserts it in its place. Depending on the source parameter the parsed CSS will be treated as rtl or ltr:

input

.test1 {
    color: #EFEFEF;
    left: 10px;
    /*rtl:raw:
    height: 50px;
    width: 100px;*/
}

/*rtl:raw:.test2 {
    color: #EFEFEF;
    left: 10px;
    width: 100%;    
}

.test3 {
    transform: translate(10px, 20px);
}
*/

output

.test1 {
    color: #EFEFEF;
}

[dir="ltr"] .test1 {
    left: 10px;
}

[dir="rtl"] .test1 {
    right: 10px;
    height: 50px;
    width: 100px;
}

[dir="rtl"] .test2 {
    color: #EFEFEF;
    left: 10px;
    width: 100%;    
}

[dir="rtl"] .test3 {
    transform: translate(10px, 20px);
}

This directive ignores processing of the current declaration:

input

.test1, .test2 {
    text-align: left /*rtl:ignore*/;
    left: 10px;
}

output

.test1, .test2 {
    text-align: left;
}

[dir="ltr"] .test1, [dir="ltr"] .test2 {
    left: 10px;
}

[dir="rtl"] .test1, [dir="rtl"] .test2 {
    right: 10px;
}

This directive appends {value} to the end of the declaration value:

input

.test1, .test2 {
    padding: 10px /*rtl:append20px*/;
    left: 10px;
}

output

[dir="ltr"] .test1, [dir="ltr"] .test2 {
    padding: 10px;
    left: 10px;
}

[dir="rtl"] .test1, [dir="rtl"] .test2 {
    padding: 10px 20px;
    right: 10px;
}

This directive inserts {value} to where the directive is located inside the declaration value:

input

.test1, .test2 {
    padding: 10px/*rtl:insert 20px*/ 5px;
    left: 10px;
}

output

[dir="ltr"] .test1, [dir="ltr"] .test2 {
    padding: 10px 5px;
    left: 10px;
}

[dir="rtl"] .test1, [dir="rtl"] .test2 {
    padding: 10px 20px 5px;
    right: 10px;
}

This directive prepends {value} to the begining of the declaration value:

input

.test1, .test2 {
    font-family: Arial, Helvetica/*rtl:prepend:"Droid Arabic Kufi", */;
    left: 10px;
}

output

[dir="ltr"] .test1, [dir="ltr"] .test2 {
    font-family: Arial, Helvetica;
    left: 10px;
}

[dir="rtl"] .test1, [dir="rtl"] .test2 {
    font-family: "Droid Arabic Kufi", Arial, Helvetica;
    right: 10px;
}

This directive replaces the declaration value with {value}:

input

.test1, .test2 {
    font-family: Arial, Helvetica/*rtl:"Droid Arabic Kufi"*/;
    left: 10px;
}

output

[dir="ltr"] .test1, [dir="ltr"] .test2 {
    font-family: Arial, Helvetica;
    left: 10px;
}

[dir="rtl"] .test1, [dir="rtl"] .test2 {
    font-family: "Droid Arabic Kufi";
    right: 10px;
}